Benzocyclooctyne compounds and uses thereof

ABSTRACT

Provided are benzocyclooctyne compounds of formula (I). These compounds undergo strain-promoted azide-alkyne cyclo additions (SPAAC) without presence of toxic metal catalysts. The provided compounds are useful for diagnosis and imaging of azide-containing molecules. Methods for detection and imaging biomolecules using compounds of the present disclosure are disclosed.

TECHNICAL FIELD OF THE PRESENT DISCLOSURE

The present disclosure relates to benzocyclooctyne compounds and their application in diagnosis and imaging of azide-containing molecules.

BACKGROUND OF THE PRESENT DISCLOSURE

Copper-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC) has gained widespread use in chemical biology for applications such as labeling of biomolecules in complex mixtures and imaging of fixed cells and tissues. (Kolb, et al., Angew. Chem. Int. Ed. 2001, 40, 2004; Rostovtsev, et al., Angew. Chem. Int. Ed. 2002, 41, 2596; Wu and Fokin, Aldrichimica Acta 2007, 40, 7.) Incorporation of fluorescent probes into proteins, DNA, RNA, lipids and glycans within their native cellular environments provides opportunities for imaging and understanding their roles in vivo. (Best, Biochemistry 2009, 48, 6571.)

For example, glycans in proteins are displayed on the cell surface with implications in numerous physiological and pathological processes. Aberrant glycosylation on the surface of diseased cells is often observed in pathological conditions, such as inflammation and cancer metastasis. In particular, altered terminal sialylation and fucosylation, which are believed to result from changes in expression locations and levels of sialyltransferases and fucosyltransferases, are associated with tumor malignancy. The ability to explore the biological information content of glycans as biomarkers of cancer, attached to either proteins or lipids, has become a major course of glycomics research. (Hsu, et al., Proc. Nat. Acad. Sci. U.S.A., 2007, 104, 2614; Sawa, et al., Proc. Nat. Acad. Sci. U.S.A., 2006, 103, 12371.)

Analysis of changes in glycosylation patterns in living systems is now possible. (Prescher and Bertozzi, Nat. Chem. Bio. 2005, 1, 13.) Metabolic incorporation of an unnatural carbohydrate containing unique functional group that acts as a bioorthogonal chemical reporter into the cell biosynthetic machinery initiates the process. The modified glycan is then processed and constructed on the cell surface. Subsequent reaction with a detectable fluorescent probe equipped with a complementary bioorthogonal functional group enables detection of the incorporated unnatural glycan (FIG. 1). (Sletten and Bertozzi, Angew. Chem. Int. Ed. 2009, 48, 6974-98.)

The concept of bioorthogonal chemical reporter has been applied to proteomic analysis of glycosylation in proteins and chemical remodeling of cell surfaces in living systems. Bioorthogonal chemical reactions have also been used for other applications, such as protein labeling, activity-based protein folding, protein targets identification, posttranslational modifications, and cell proliferation monitoring. Labeling of specific functional groups on living cell via bioorthogonal chemical reporter strategies have become increasingly powerful in cell biology. These approaches are often based on cycloadditions as ideal bioorthogonal reactions because of their intrinsic selectivity and tunable electronics. However, there are still many challenges facing the field. For example, most bioorthogonal reporter strategies entail multistep procedures that use fluorophroe-labeled reactant partners, which often cause high background fluorescent noise that is difficult to remove from intracellular environments or tissues. In addition, these methods require high concentrations of reagents and catalysts in order to achieve detectable signals.

Some recent efforts have been focused on the design of fluorogenic CuAAC reactions between non-fluorescent alkyne and azide, which can ligate to afford a highly fluorescent triazole complex (FIG. 1). (Sivakumar, et al., Org. Lett. 2004, 24, 4603; Sawa, et al., Proc. Nat. Acad. Sci. U.S.A., 2006, 103, 12371; Xie, et al., Tetrahedron 2008, 64, 2906; Li, et al., Org. Lett. 2009, 11, 3008; Le Droumaguet, et al., Chem. Soc. Rev. 2010, 39, 1223; Chao, et al., Sci. China Chemistry 2012, 55, 125.) This type of CuAAC reaction occurring in high efficiency would have broad applications in the emerging field of cell biology and functional proteomics due to the distinct fluorescence properties in formation of the triazole without background fluorescent noise of the starting materials. Unfortunately, the use of CuAAC reactions in living systems has been hindered because the reactions require toxic copper(I) ion as the catalyst.

To circumvent the cytotoxicity associated with metal catalyst, the ring strain-promoted azide-alkyne cycloadditions (SPAAC) without using metal catalyst have been developed. (Agard, et al., J. Am. Chem. Soc. 2004, 126, 15046; Codelli, et al., J. Am. Chem. Soc. 2008, 130, 11486; Debets, et al., Acc. Chem. Res. 2011, 44, 805; Dommerholt, et al., Angew. Chem. Int. Ed. 2010, 49, 9422; Friscourt, et al., J. Am. Chem. Soc. 2012, 134, 5381; Jewett, et al., J. Am. Chem. Soc. 2010, 132, 3688; Ning, et al., Angew. Chem. Int. Ed. 2008, 47, 2253; Poloukhtine, et al., J. Am. Chem. Soc. 2009, 131, 15769; Varga, et al., Chem. Eur. J. 2012, 18, 822.) A cyclooctyne moiety is often incorporated as a stem structure into the SPAAC reagents, such as difluorinated cyclooctynes (DIFO) and the derivatives. An attempt toward this approach was reported by Bertozzi and co-workers using the biarylazacyclooctynone ring fused with a coumarin fluorophore (J. C. Jewett, C. R. Bertozzi, Org. Lett. 2011, 13, 5937-5939). Although the compound undergoes a cycloaddition reaction with 2-azidoethanol to give a 10-fold increase in fluorescence intensity, the triazole product exhibited a low quantum yield (Φ_(f)=0.04) and required relatively high energy excitation (˜300 nm), making it unsuitable for imaging in living systems.

SUMMARY OF THE PRESENT DISCLOSURE

The present disclosure relates to novel benzocyclooctyne compounds of formula (I) that undergo strain-promoted azide-alkyne cycloadditions (SPAAC) without using toxic metal catalyst. Exemplary coumarin-cyclooctyne compounds according to the present disclosure react with azide compounds to give the triazole products with enhanced fluorescence to facilitate the detection and imaging. The provided compounds represent a significant advance in live-cell imaging and are applicable to real-time detection of biochemical events in vivo.

One aspect of the present disclosure relates to a compound of Formula (I):

or a salt thereof, wherein X¹, X², X³, X⁴, G¹, G², G³, G⁴, G⁵, G⁶, G⁷ and G⁸ are as described herein.

In some embodiments, the compound is of formula (II).

or a salt thereof, wherein X¹, X², X³, X⁴, G¹, G², G³, G⁴, G⁵, G⁶, G⁷, G⁸, G⁹ and G¹⁰ are as described herein.

In certain embodiments, the provided compound is Compound 1 or Compound 2 shown below:

or a salt thereof.

In another aspect, the present disclosure present disclosure provides synthetic methods for preparation of benzocyclooctyne compounds. The present disclosure also demonstrates that the benzocyclooctyne compounds described herein react with organic azides to form triazole products with enhanced fluorescence.

In yet another aspect, present disclosure the present disclosure relates to methods for detecting and/or imaging biomolecules.

In certain embodiments, the present disclosure present disclosure provides a method for imaging an azide-containing molecule, the method comprising

-   -   (a) incubating a compound as described herein with a sample         containing the azide-containing molecule under conditions         allowing for ligation of the compound to an azido group of the         molecule to form a triazole product; and     -   (b) detecting a fluorescent signal released from the triazole         product.

In certain embodiments, the present disclosure present disclosure provides a method for detecting an azide-containing molecule in a sample, the method comprising:

(a) contacting a compound as described herein to a sample suspected of having an azide-containing molecule;

(b) detecting a level of a fluorescent signal released from the sample, and

(c) determining presence of the azide-containing molecule in the sample, wherein an enhanced fluorescent signal as compared to a level of the fluorescent signal in the absence of the compound indicates presence of the azide-containing molecule.

In certain embodiments, the compound used in the methods of imaging or detecting an azide-containing molecule as described herein is Compound 1 or Compound 2, or a salt thereof.

DEFINITIONS

Definitions of specific functional groups and chemical terms are described in more detail below. The chemical elements are identified in accordance with the Periodic Table of the Elements, CAS version, Handbook of Chemistry and Physics, 75^(th) Ed., inside cover, and specific functional groups are generally defined as described therein. Additionally, general principles of organic chemistry, as well as specific functional moieties and reactivity, are described in Organic Chemistry, Thomas Sorrell, University Science Books, Sausalito, 1999; Smith and March March's Advanced Organic Chemistry, 5^(th) Edition, John Wiley & Sons, Inc., New York, 2001; Larock, Comprehensive Organic Transformations, VCH Publishers, Inc., New York, 1989; and Carruthers, Some Modern Methods of Organic Synthesis, 3^(rd) Edition, Cambridge University Press, Cambridge, 1987.

Compounds described herein can comprise one or more asymmetric centers, and thus can exist in various stereoisomeric forms, e.g., enantiomers and/or diastereomers. For example, the compounds described herein can be in the form of an individual enantiomer, diastereomer or geometric isomer, or can be in the form of a mixture of stereoisomers, including racemic mixtures and mixtures enriched in one or more stereoisomer. Isomers can be isolated from mixtures by methods known to those skilled in the art, including chiral high pressure liquid chromatography (HPLC) and the formation and crystallization of chiral salts; or preferred isomers can be prepared by asymmetric syntheses. See, for example, Jacques et al., Enantiomers, Racemates and Resolutions (Wiley Interscience, New York, 1981); Wilen et al., Tetrahedron 33:2725 (1977); Eliel, E. L. Stereochemistry of Carbon Compounds (McGraw-Hill, NY, 1962); and Wilen, S. H. Tables of Resolving Agents and Optical Resolutions p. 268 (E. L. Eliel, Ed., Univ. of Notre Dame Press, Notre Dame, Ind. 1972). The present disclosure additionally encompasses compounds as individual isomers substantially free of other isomers, and alternatively, as mixtures of various isomers.

When a range of values is listed, it is intended to encompass each value and sub-range within the range. For example “C₁₋₆ alkyl” is intended to encompass, C₁, C₂, C₃, C₄, C₅, C₆, C₁₋₆, C₁₋₅, C₁₋₄, C₁₋₃, C₁₋₂, C₂₋₆, C₂₋₅, C₂₋₄, C₂₋₃, C₃₋₆, C₃₋₅, C₃₋₄, C₄₋₆, C₄₋₅, and C₅₋₆ alkyl.

As used herein, “alkyl” refers to a radical of a straight-chain or branched saturated hydrocarbon group having from 1 to 10 carbon atoms (“C₁₋₁₀ alkyl”). In some embodiments, an alkyl group has 1 to 9 carbon atoms (“C₁₋₉ alkyl”). In some embodiments, an alkyl group has 1 to 8 carbon atoms (“C₁₋₈ alkyl”). In some embodiments, an alkyl group has 1 to 7 carbon atoms (“C₁₋₇ alkyl”). In some embodiments, an alkyl group has 1 to 6 carbon atoms (“C₁₋₆ alkyl”). In some embodiments, an alkyl group has 1 to 5 carbon atoms (“C₁₋₅ alkyl”). In some embodiments, an alkyl group has 1 to 4 carbon atoms (“C₁₋₄ alkyl”). In some embodiments, an alkyl group has 1 to 3 carbon atoms (“C₁₋₃ alkyl”). In some embodiments, an alkyl group has 1 to 2 carbon atoms (“C₁₋₂ alkyl”). In some embodiments, an alkyl group has 1 carbon atom (“C₁ alkyl”). In some embodiments, an alkyl group has 2 to 6 carbon atoms (“C₂₋₆ alkyl”). Examples of C₁₋₆ alkyl groups include methyl (C₁), ethyl (C₂), n-propyl (C₃), isopropyl (C₃), n-butyl (C₄), tert-butyl (C₄), sec-butyl (C₄), iso-butyl (C₄), n-pentyl (C₅), 3-pentanyl (C₅), amyl (C₅), neopentyl (C₅), 3-methyl-2-butanyl (C₅), tertiary amyl (C₅), and n-hexyl (C₆). Additional examples of alkyl groups include n-heptyl (C₇), n-octyl (C₈) and the like. Unless otherwise specified, each instance of an alkyl group is independently unsubstituted (an “unsubstituted alkyl”) or substituted (a “substituted alkyl”) with one or more substituents. In certain embodiments, the alkyl group is an unsubstituted C₁₋₁₀ alkyl (e.g., —CH₃). In certain embodiments, the alkyl group is a substituted C₁₋₁₀ alkyl.

As used herein, “alkenyl” refers to a radical of a straight-chain or branched hydrocarbon group having from 2 to 10 carbon atoms and one or more carbon-carbon double bonds (e.g., 1, 2, 3, or 4 double bonds). In some embodiments, an alkenyl group has 2 to 9 carbon atoms (“C₂₋₉ alkenyl”). In some embodiments, an alkenyl group has 2 to 8 carbon atoms (“C₂₋₈ alkenyl”). In some embodiments, an alkenyl group has 2 to 7 carbon atoms (“C₂₋₇ alkenyl”). In some embodiments, an alkenyl group has 2 to 6 carbon atoms (“C₂₋₆ alkenyl”). In some embodiments, an alkenyl group has 2 to 5 carbon atoms (“C₂₋₅ alkenyl”). In some embodiments, an alkenyl group has 2 to 4 carbon atoms (“C₂₋₄ alkenyl”). In some embodiments, an alkenyl group has 2 to 3 carbon atoms (“C₂₋₃ alkenyl”). In some embodiments, an alkenyl group has 2 carbon atoms (“C₂ alkenyl”). The one or more carbon-carbon double bonds can be internal (such as in 2-butenyl) or terminal (such as in 1-butenyl). Examples of C₂₋₄ alkenyl groups include ethenyl (C₂), 1-propenyl (C₃), 2-propenyl (C₃), 1-butenyl (C₄), 2-butenyl (C₄), butadienyl (C₄), and the like. Examples of C₂₋₆ alkenyl groups include the aforementioned C₂₋₄ alkenyl groups as well as pentenyl (C₅), pentadienyl (C₅), hexenyl (C₆), and the like. Additional examples of alkenyl include heptenyl (C₇), octenyl (C₈), octatrienyl (C₈), and the like. Unless otherwise specified, each instance of an alkenyl group is independently unsubstituted (an “unsubstituted alkenyl”) or substituted (a “substituted alkenyl”) with one or more substituents. In certain embodiments, the alkenyl group is an unsubstituted C₂₋₁₀ alkenyl. In certain embodiments, the alkenyl group is a substituted C₂₋₁₀ alkenyl.

As used herein, “alkynyl” refers to a radical of a straight-chain or branched hydrocarbon group having from 2 to 10 carbon atoms and one or more carbon-carbon triple bonds (e.g., 1, 2, 3, or 4 triple bonds) (“C₂₋₁₀ alkynyl”). In some embodiments, an alkynyl group has 2 to 9 carbon atoms (“C₂₋₉ alkynyl”). In some embodiments, an alkynyl group has 2 to 8 carbon atoms (“C₂₋₈ alkynyl”). In some embodiments, an alkynyl group has 2 to 7 carbon atoms (“C₂₋₇ alkynyl”). In some embodiments, an alkynyl group has 2 to 6 carbon atoms (“C₂₋₆ alkynyl”). In some embodiments, an alkynyl group has 2 to 5 carbon atoms (“C₂₋₅ alkynyl”). In some embodiments, an alkynyl group has 2 to 4 carbon atoms (“C₂₋₄ alkynyl”). In some embodiments, an alkynyl group has 2 to 3 carbon atoms (“C₂₋₃ alkynyl”). In some embodiments, an alkynyl group has 2 carbon atoms (“C₂ alkynyl”). The one or more carbon-carbon triple bonds can be internal (such as in 2-butynyl) or terminal (such as in 1-butynyl). Examples of C₂₋₄ alkynyl groups include, without limitation, ethynyl (C₂), 1-propynyl (C₃), 2-propynyl (C₃), 1-butynyl (C₄), 2-butynyl (C₄), and the like. Examples of C₂₋₆ alkenyl groups include the aforementioned C₂₋₄ alkynyl groups as well as pentynyl (C₅), hexynyl (C₆), and the like. Additional examples of alkynyl include heptynyl (C₇), octynyl (C₈), and the like. Unless otherwise specified, each instance of an alkynyl group is independently unsubstituted (an “unsubstituted alkynyl”) or substituted (a “substituted alkynyl”) with one or more substituents. In certain embodiments, the alkynyl group is an unsubstituted C₂₋₁₀ alkynyl. In certain embodiments, the alkynyl group is a substituted C₂₋₁₀ alkynyl.

As used herein, “carbocyclyl” or “carbocyclic” refers to a radical of a non-aromatic cyclic hydrocarbon group having from 3 to 10 ring carbon atoms (“C₃₋₁₀ carbocyclyl”) and zero heteroatoms in the non-aromatic ring system. In some embodiments, a carbocyclyl group has 3 to 8 ring carbon atoms (“C₃₋₈ carbocyclyl”). In some embodiments, a carbocyclyl group has 3 to 7 ring carbon atoms (“C₃₋₇ carbocyclyl”). In some embodiments, a carbocyclyl group has 3 to 6 ring carbon atoms (“C₃₋₆ carbocyclyl”). In some embodiments, a carbocyclyl group has 4 to 6 ring carbon atoms (“C₄₋₆ carbocyclyl”). In some embodiments, a carbocyclyl group has 5 to 6 ring carbon atoms (“C₅₋₆ carbocyclyl”). In some embodiments, a carbocyclyl group has 5 to 10 ring carbon atoms (“C₅₋₁₀ carbocyclyl”). Exemplary C₃₋₆ carbocyclyl groups include, without limitation, cyclopropyl (C₃), cyclopropenyl (C₃), cyclobutyl (C₄), cyclobutenyl (C₄), cyclopentyl (C₅), cyclopentenyl (C₅), cyclohexyl (C₆), cyclohexenyl (C₆), cyclohexadienyl (C₆), and the like. Exemplary C₃₋₈ carbocyclyl groups include, without limitation, the aforementioned C₃₋₆ carbocyclyl groups as well as cycloheptyl (C₇), cycloheptenyl (C₇), cycloheptadienyl (C₇), cycloheptatrienyl (C₇), cyclooctyl (C₈), cyclooctenyl (C₈), bicyclo[2.2.1]heptanyl (C₇), bicyclo[2.2.2]octanyl (C₈), and the like. Exemplary C₃₋₁₀ carbocyclyl groups include, without limitation, the aforementioned C₃₋₈ carbocyclyl groups as well as cyclononyl (C₉), cyclononenyl (C₉), cyclodecyl (C₁₀), cyclodecenyl (C₁₀), octahydro-1H-indenyl (C₉), decahydronaphthalenyl (C₁₀), spiro[4.5]decanyl (C₁₀), and the like. As the foregoing examples illustrate, in certain embodiments, the carbocyclyl group is either monocyclic (“monocyclic carbocyclyl”) or polycyclic (e.g., containing a fused, bridged or spiro ring system such as a bicyclic system (“bicyclic carbocyclyl”) or tricyclic system (“tricyclic carbocyclyl”)) and can be saturated or can contain one or more carbon-carbon double or triple bonds. “Carbocyclyl” also includes ring systems wherein the carbocyclyl ring, as defined above, is fused with one or more aryl or heteroaryl groups wherein the point of attachment is on the carbocyclyl ring, and in such instances, the number of carbons continue to designate the number of carbons in the carbocyclic ring system. Unless otherwise specified, each instance of a carbocyclyl group is independently unsubstituted (an “unsubstituted carbocyclyl”) or substituted (a “substituted carbocyclyl”) with one or more substituents. In certain embodiments, the carbocyclyl group is an unsubstituted C₃₋₁₀ carbocyclyl. In certain embodiments, the carbocyclyl group is a substituted C₃₋₁₀ carbocyclyl.

As used herein, “heterocyclyl” or “heterocyclic” refers to a radical of a 3- to 14-membered non-aromatic ring system having ring carbon atoms and 1 to 4 ring heteroatoms, wherein each heteroatom is independently selected from nitrogen, oxygen, and sulfur (“3-14 membered heterocyclyl”). In heterocyclyl groups that contain one or more nitrogen atoms, the point of attachment can be a carbon or nitrogen atom, as valency permits. A heterocyclyl group can either be monocyclic (“monocyclic heterocyclyl”) or polycyclic (e.g., a fused, bridged or spiro ring system such as a bicyclic system (“bicyclic heterocyclyl”) or tricyclic system (“tricyclic heterocyclyl”)), and can be saturated or can contain one or more carbon-carbon double or triple bonds. Heterocyclyl polycyclic ring systems can include one or more heteroatoms in one or both rings. “Heterocyclyl” also includes ring systems wherein the heterocyclyl ring, as defined above, is fused with one or more carbocyclyl groups wherein the point of attachment is either on the carbocyclyl or heterocyclyl ring, or ring systems wherein the heterocyclyl ring, as defined above, is fused with one or more aryl or heteroaryl groups, wherein the point of attachment is on the heterocyclyl ring, and in such instances, the number of ring members continue to designate the number of ring members in the heterocyclyl ring system. Unless otherwise specified, each instance of heterocyclyl is independently unsubstituted (an “unsubstituted heterocyclyl”) or substituted (a “substituted heterocyclyl”) with one or more substituents. In certain embodiments, the heterocyclyl group is an unsubstituted 3-14 membered heterocyclyl. In certain embodiments, the heterocyclyl group is a substituted 3-14 membered heterocyclyl.

As used herein, “aryl” refers to a radical of a monocyclic or polycyclic (e.g., bicyclic or tricyclic) 4n+2 aromatic ring system (e.g., having 6, 10, or 14 it electrons shared in a cyclic array) having 6-14 ring carbon atoms and zero heteroatoms provided in the aromatic ring system (“C₆₋₁₄ aryl”). In some embodiments, an aryl group has 6 ring carbon atoms (“C₆ aryl”; e.g., phenyl). In some embodiments, an aryl group has 10 ring carbon atoms (“C₁₀ aryl”; e.g., naphthyl such as 1-naphthyl and 2-naphthyl). In some embodiments, an aryl group has 14 ring carbon atoms (“C₁₄ aryl”; e.g., anthracyl). “Aryl” also includes ring systems wherein the aryl ring, as defined above, is fused with one or more carbocyclyl or heterocyclyl groups wherein the radical or point of attachment is on the aryl ring, and in such instances, the number of carbon atoms continue to designate the number of carbon atoms in the aryl ring system. Unless otherwise specified, each instance of an aryl group is independently unsubstituted (an “unsubstituted aryl”) or substituted (a “substituted aryl”) with one or more substituents. In certain embodiments, the aryl group is an unsubstituted C₆₋₁₄ aryl. In certain embodiments, the aryl group is a substituted C₆₋₁₄ aryl.

As used herein, “heteroaryl” refers to a radical of a 5-14 membered monocyclic or polycyclic (e.g., bicyclic, tricyclic) 4n+2 aromatic ring system (e.g., having 6, 10, or 14 it electrons shared in a cyclic array) having ring carbon atoms and 1-4 ring heteroatoms provided in the aromatic ring system, wherein each heteroatom is independently selected from nitrogen, oxygen and sulfur (“5-14 membered heteroaryl”). In heteroaryl groups that contain one or more nitrogen atoms, the point of attachment can be a carbon or nitrogen atom, as valency permits. Heteroaryl polycyclic ring systems can include one or more heteroatoms in one or both rings. “Heteroaryl” includes ring systems wherein the heteroaryl ring, as defined above, is fused with one or more carbocyclyl or heterocyclyl groups wherein the point of attachment is on the heteroaryl ring, and in such instances, the number of ring members continue to designate the number of ring members in the heteroaryl ring system. “Heteroaryl” also includes ring systems wherein the heteroaryl ring, as defined above, is fused with one or more aryl groups wherein the point of attachment is either on the aryl or heteroaryl ring, and in such instances, the number of ring members designates the number of ring members in the fused polycyclic (aryl/heteroaryl) ring system. Polycyclic heteroaryl groups wherein one ring does not contain a heteroatom (e.g., indolyl, quinolinyl, carbazolyl, and the like) the point of attachment can be on either ring, i.e., either the ring bearing a heteroatom (e.g., 2-indolyl) or the ring that does not contain a heteroatom (e.g., 5-indolyl).

As understood from the above, alkyl, alkenyl, alkynyl, heteroalkyl, heteroalkenyl, heteroalkynyl, carbocyclyl, heterocyclyl, aryl, and heteroaryl groups, as defined herein, are, in certain embodiments, optionally substituted. Optionally substituted refers to a group which may be substituted or unsubstituted (e.g., “substituted” or “unsubstituted” alkyl, “substituted” or “unsubstituted” alkenyl, “substituted” or “unsubstituted” alkynyl, “substituted” or “unsubstituted” heteroalkyl, “substituted” or “unsubstituted” heteroalkenyl, “substituted” or “unsubstituted” heteroalkynyl, “substituted” or “unsubstituted” carbocyclyl, “substituted” or “unsubstituted” heterocyclyl, “substituted” or “unsubstituted” aryl or “substituted” or “unsubstituted” heteroaryl group). In general, the term “substituted” means that at least one hydrogen present on a group is replaced with a permissible substituent, e.g., a substituent which upon substitution results in a stable compound, e.g., a compound which does not spontaneously undergo transformation such as by rearrangement, cyclization, elimination, or other reaction. Unless otherwise indicated, a “substituted” group has a substituent at one or more substitutable positions of the group, and when more than one position in any given structure is substituted, the substituent is either the same or different at each position. The term “substituted” is contemplated to include substitution with all permissible substituents of organic compounds, any of the substituents described herein that results in the formation of a stable compound. The present present disclosure contemplates any and all such combinations in order to arrive at a stable compound. For purposes of this present disclosure, heteroatoms such as nitrogen may have hydrogen substituents and/or any suitable substituent as described herein which satisfy the valencies of the heteroatoms and results in the formation of a stable moiety.

Exemplary carbon atom substituents include, but are not limited to, halogen, —CN, —NO₂, —N₃, —SO₂H, —SO₃H, —OH, —OR^(aa), —ON(R^(bb))₂, —N(R^(bb))₂, —N(R^(bb))₃ ⁺X⁻, —N(OR^(cc))R^(bb), —SH, —SR^(aa), —SSR^(cc), —C(═O)R^(aa), —CO₂H, —CHO, —C(OR^(cc))₂, —CO₂R^(aa), —OC(═O)R^(aa), —OCO₂R^(aa), —C(═O)N(R^(bb))₂, —OC(═O)N(R^(bb))₂, —NR^(bb)C(═O)R^(aa), —NR^(bb)CO₂R^(aa), —NR^(bb)C(═O)N(R^(bb)) ₂, —C(═NR^(bb))R^(aa), —C(═NR^(bb))OR^(aa), —OC(═NR^(bb))R^(aa), —OC(═NR^(bb))OR^(aa), —C(═NR^(bb))N(R^(bb))₂, —OC(═NR^(bb))N(R^(bb))₂, —NR^(bb)C(═NR^(bb))N(R^(bb))₂, —C(═O)NR^(bb)SO₂R^(aa), —NR^(bb)SO₂R^(aa), —SO₂N(R^(bb))₂, —SO₂R^(aa), —SO₂OR^(aa), —OSO₂R^(aa), —S(═O)R^(aa), —OS(═O)R^(aa), —Si(R^(aa))₃, —OSi(R^(aa))₃—C(═S)N(R^(bb))₂, —C(═O)SR^(aa), —C(═S)SR^(aa), —SC(═S)SR^(aa), —SC(═O)SR^(aa), —OC(═O)SR^(aa), —SC(═O)OR^(aa), —SC(═O)R^(aa), —P(═O)₂R^(aa), —OP(═O)₂R^(aa), —P(═O)(R^(aa))₂, —OP(═O)(R^(aa))₂, —OP(═O)(OR^(cc))₂, —P(═O)₂N(R^(bb))₂, —OP(═O)₂N(R^(bb))₂, —P(═O)(NR^(bb))₂, —OP(═O)(NR^(bb))₂, —NR^(bb)P(═O)(OR^(cc))₂, —NR^(bb)P(═O)(NR^(bb))₂, —P(R^(cc))₂, —P(R^(cc))₃, —OP(R^(cc))₂, —OP(R^(cc))₃, —B(R^(aa))₂, —B(OR^(cc))₂, —BR^(aa)(OR^(cc)), C₁₋₁₀ alkyl, C₁₋₁₀ perhaloalkyl, C₂₋₁₀ alkenyl, C₂₋₁₀ alkynyl, C₁₋₁₀ heteroalkyl, C₂₋₁₀ heteroalkenyl, C₂₋₁₀heteroalkynyl, C₃₋₁₄ carbocyclyl, 3-14 membered heterocyclyl, C₆₋₁₄ aryl, and 5-14 membered heteroaryl, wherein each alkyl, alkenyl, alkynyl, heteroalkyl, heteroalkenyl, heteroalkynyl, carbocyclyl, heterocyclyl, aryl, and heteroaryl is independently substituted with 0, 1, 2, 3, 4, or 5 R^(dd) groups;

or two geminal hydrogens on a carbon atom are replaced with the group ═O, ═S, ═NN(R^(bb))₂, ═NNR^(bb)C(═O)R^(aa), ═NNR^(bb)C(═O)OR^(aa), ═NNR^(bb)S(═O)₂R^(aa), ═NR^(bb), or ═NOR^(cc);

each instance of R^(aa) is, independently, selected from C₁₋₁₀ alkyl, C₁₋₁₀ perhaloalkyl, C₂₋₁₀ alkenyl, C₂₋₁₀ alkynyl, C₁₋₁₀ heteroalkyl, C₂₋₁₀ heteroalkenyl, C₂₋₁₀heteroalkynyl, C₃₋₁₀ carbocyclyl, 3-14 membered heterocyclyl, C₆₋₁₄ aryl, and 5-14 membered heteroaryl, or two R^(aa) groups are joined to form a 3-14 membered heterocyclyl or 5-14 membered heteroaryl ring, wherein each alkyl, alkenyl, alkynyl, heteroalkyl, heteroalkenyl, heteroalkynyl, carbocyclyl, heterocyclyl, aryl, and heteroaryl is independently substituted with 0, 1, 2, 3, 4, or 5 R^(dd) groups;

each instance of R^(bb) is, independently, selected from hydrogen, —OH, —OR^(aa), —N(R^(cc))₂, —CN, —C(═O)R^(aa), —C(═O)N(R^(cc))₂, —CO₂R^(aa), —SO₂R^(aa), —C(═NR^(cc))OR^(aa), —C(═NR^(cc))N(R^(cc))₂, —SO₂N(R^(cc))₂, —SO₂R, —SO₂OR^(cc), —SOR^(aa), —C(═S)N(R^(cc))₂, —C(═O)SR^(cc), —C(═S)SR^(cc), —P(═O)₂R^(aa), —P(═O)(R^(aa))₂, —P(═O)₂N(R^(cc))₂, —P(═O)(NR^(cc))₂, C₁₋₁₀ alkyl, C₁₋₁₀ perhaloalkyl, C₂₋₁₀ alkenyl, C₂₋₁₀ alkynyl, C₁₋₁₀ heteroalkyl, C₂₋₁₀ heteroalkenyl, C₂₋₁₀heteroalkynyl, C₃₋₁₀ carbocyclyl, 3-14 membered heterocyclyl, C₆₋₁₄ aryl, and 5-14 membered heteroaryl, or two R^(bb) groups are joined to form a 3-14 membered heterocyclyl or 5-14 membered heteroaryl ring, wherein each alkyl, alkenyl, alkynyl, heteroalkyl, heteroalkenyl, heteroalkynyl, carbocyclyl, heterocyclyl, aryl, and heteroaryl is independently substituted with 0, 1, 2, 3, 4, or 5 R^(dd) groups;

each instance of R^(cc) is, independently, selected from hydrogen, C₁₋₁₀ alkyl, C₁₋₁₀ perhaloalkyl, C₂₋₁₀ alkenyl, C₂₋₁₀ alkynyl, C₁₋₁₀ heteroalkyl, C₂₋₁₀ heteroalkenyl, C₂₋₁₀ heteroalkynyl, C₃₋₁₀ carbocyclyl, 3-14 membered heterocyclyl, C₆₋₁₄ aryl, and 5-14 membered heteroaryl, or two R^(cc) groups are joined to form a 3-14 membered heterocyclyl or 5-14 membered heteroaryl ring, wherein each alkyl, alkenyl, alkynyl, heteroalkyl, heteroalkenyl, heteroalkynyl, carbocyclyl, heterocyclyl, aryl, and heteroaryl is independently substituted with 0, 1, 2, 3, 4, or 5 R^(dd) groups;

each instance of R^(dd) is, independently, selected from halogen, —CN, —NO₂, —N₃, —SO₂H, —SO₃H, —OH, —OR^(ee), —ON(R^(ff))₂, —N(R^(ff))₂, —N(R^(ff))₃ ⁺X⁻, —N(OR^(ee))R^(ff), —SH, —SR^(ee), —SSR^(ee), —C(═O)R^(ee), —CO₂H, —CO₂R^(ee), —OC(═O)R^(ee), —OCO₂R^(ee), —C(═O)N(R^(ff))₂, —OC(═O)N(R^(ff))₂, —NR^(ff)C(═O)R^(ee), —NR^(ff)CO₂R^(ee), —NR^(ff)C(═O)N(R^(ff))₂, —C(═NR^(ff))OR^(ee), —OC(═NR^(ff))R^(ee), —OC(═NR^(ff))OR^(ee), —C(═NR^(ff))N(R^(ff))₂, —OC(═NR^(ff))N(R^(ff))₂, —NR^(ff)C(═NR^(ff))N(R^(ff))₂, —NR^(ff)SO₂R^(ee), —SO₂N(R^(ff))₂, —SO₂R^(ee), —SO₂OR^(ee), —OSO₂R^(ee), —S(═O)R^(ee), —Si(R^(ee))₃, —OSi(R^(ee))₃, —C(═S)N(R^(ff))₂, —C(═O)SR^(ee), —C(═S)SR^(ee), —SC(═S)SR^(ee), —P(═O)₂R^(ee), —P(═O)(R^(ee))₂, —OP(═O)(R^(ee))₂, —OP(═O)(OR^(ee))₂, C₁₋₆ alkyl, C₁₋₆ perhaloalkyl, C₂₋₆ alkenyl, C₂₋₆ alkynyl, C₁₋₆ heteroalkyl, C₂₋₆ heteroalkenyl, C₂₋₆heteroalkynyl, C₃₋₁₀ carbocyclyl, 3-10 membered heterocyclyl, C₆₋₁₀ aryl, 5-10 membered heteroaryl, wherein each alkyl, alkenyl, alkynyl, heteroalkyl, heteroalkenyl, heteroalkynyl, carbocyclyl, heterocyclyl, aryl, and heteroaryl is independently substituted with 0, 1, 2, 3, 4, or 5 R^(gg) groups, or two geminal R^(dd) substituents can be joined to form ═O or ═S;

each instance of R^(ee) is, independently, selected from C₁₋₆ alkyl, C₁₋₆ perhaloalkyl, C₂₋₆ alkenyl, C₂₋₆ alkynyl, C₁₋₆ heteroalkyl, C₂₋₆ heteroalkenyl, C₂₋₆heteroalkynyl, C₃₋₁₀ carbocyclyl, C₆₋₁₀ aryl, 3-10 membered heterocyclyl, and 3-10 membered heteroaryl, wherein each alkyl, alkenyl, alkynyl, heteroalkyl, heteroalkenyl, heteroalkynyl, carbocyclyl, heterocyclyl, aryl, and heteroaryl is independently substituted with 0, 1, 2, 3, 4, or 5 R^(gg) groups;

each instance of R^(ff) is, independently, selected from hydrogen, C₁₋₆ alkyl, C₁₋₆ perhaloalkyl, C₂₋₆ alkenyl, C₂₋₆ alkynyl, C₁₋₆ heteroalkyl, C₂₋₆ heteroalkenyl, C₂₋₆heteroalkynyl, C₃₋₁₀ carbocyclyl, 3-10 membered heterocyclyl, C₆₋₁₀ aryl and 5-10 membered heteroaryl, or two R^(ff) groups are joined to form a 3-14 membered heterocyclyl or 5-14 membered heteroaryl ring, wherein each alkyl, alkenyl, alkynyl, heteroalkyl, heteroalkenyl, heteroalkynyl, carbocyclyl, heterocyclyl, aryl, and heteroaryl is independently substituted with 0, 1, 2, 3, 4, or 5 R^(gg) groups; and

each instance of R^(gg) is, independently, halogen, —CN, —NO₂, —N₃, —SO₂H, —SO₃H, —OH, —OC₁₋₆ alkyl, —ON(C₁₋₆ alkyl)₂, —N(C₁₋₆ alkyl)₂, —N(C₁₋₆ alkyl)₃ ⁺X⁻, —NH(C₁₋₆ alkyl)₂ ⁺X⁻, —NH₂(C₁₋₆ alkyl)⁺X⁻, —NH₃ ⁺X⁻, —N(OC₁₋₆ alkyl)(C₁₋₆ alkyl), —N(OH)(C₁₋₆ alkyl), —NH(OH), —SH, —SC₁₋₆ alkyl, —SS(C₁₋₆ alkyl), —C(═O)(C₁₋₆ alkyl), —CO₂H, —CO₂(C₁₋₆ alkyl), —OC(═O)(C₁₋₆ alkyl), —OCO₂(C₁₋₆alkyl), —C(═O)NH₂, —C(═O)N(C₁₋₆ alkyl)₂, —OC(═O)NH(C₁₋₆ alkyl), —NHC(═O)(C₁₋₆alkyl), —N(C₁₋₆ alkyl)C(═O)(C₁₋₆ alkyl), —NHCO₂(C₁₋₆ alkyl), —NHC(═O)N(C₁₋₆ alkyl)₂, —NHC(═O)NH(C₁₋₆ alkyl), —NHC(═O)NH₂, —C(═NH)O(C₁₋₆alkyl), —OC(═NH)(C₁₋₆alkyl), —OC(═NH)OC₁₋₆ alkyl, —C(═NH)N(C₁₋₆ alkyl)₂, —C(═NH)NH(C₁₋₆ alkyl), —C(═NH)NH₂, —OC(═NH)N(C₁₋₆ alkyl)₂, —OC(NH)NH(C₁₋₆alkyl), —OC(NH)NH₂, —NHC(NH)N(C₁₋₆ alkyl)₂, —NHC(═NH)NH₂, —NHSO₂(C₁₋₆ alkyl), —SO₂N(C₁₋₆ alkyl)₂, —SO₂NH(C₁₋₆ alkyl), —SO₂NH₂, —SO₂C₁₋₆ alkyl, —SO₂OC₁₋₆ alkyl, —OSO₂C₁₋₆ alkyl, —SOC₁₋₆ alkyl, —Si(C₁₋₆ alkyl)₃, —OSi(C₁₋₆ alkyl)₃—C(═S)N(C₁₋₆ alkyl)₂, C(═S)NH(C₁₋₆ alkyl), C(═S)NH₂, —C(═O)S(C₁₋₆ alkyl), —C(═S)SC₁₋₆ alkyl, —SC(═S)SC₁₋₆ alkyl, —P(═O)₂(C₁₋₆ alkyl), —P(═O)(C₁₋₆ alkyl)₂, —OP(═O)(C₁₋₆ alkyl)₂, —OP(═O)(OC₁₋₆ alkyl)₂, C₁₋₆ alkyl, C₁₋₆ perhaloalkyl, C₂₋₆ alkenyl, C₂₋₆ alkynyl, C₁₋₆ heteroalkyl, C₂₋₆ heteroalkenyl, C₂₋₆ heteroalkynyl, C₃₋₁₀ carbocyclyl, C₆₋₁₀ aryl, 3-10 membered heterocyclyl, 5-10 membered heteroaryl; or two geminal R^(gg) substituents can be joined to form ═O or ═S; wherein X⁻ is a counterion.

As used herein, the term “halo” or “halogen” refers to fluorine (fluoro, —F), chlorine (chloro, —Cl), bromine (bromo, —Br), or iodine (iodo, —I).

In certain embodiments, the substituent present on the nitrogen atom is an nitrogen protecting group (also referred to herein as an “amino protecting group”). Nitrogen protecting groups include, but are not limited to, —OH, —OR^(aa), —N(R^(cc))₂, —C(═O)R^(aa), —C(═O)N(R^(cc))₂, —CO₂R^(aa), —SO₂R^(aa), —C(═NR^(cc))R^(aa), —C(═NR^(cc))OR^(aa), —C(═NR^(cc))N(R^(cc))₂, —SO₂N(R^(cc))₂, —SO₂R^(cc), —SO₂OR^(cc), —SOR^(aa), —C(═S)N(R^(cc))₂, —C(═O)SR^(cc), —C(═S)SR^(cc), C₁₋₁₀ alkyl (e.g., aralkyl, heteroaralkyl), C₂₋₁₀ alkenyl, C₂₋₁₀ alkynyl, C₁₋₁₀ heteroalkyl, C₂₋₁₀ heteroalkenyl, C₂₋₁₀ heteroalkynyl, C₃₋₁₀ carbocyclyl, 3-14 membered heterocyclyl, C₆₋₁₄ aryl, and 5-14 membered heteroaryl groups, wherein each alkyl, alkenyl, alkynyl, heteroalkyl, heteroalkenyl, heteroalkynyl, carbocyclyl, heterocyclyl, aralkyl, aryl, and heteroaryl is independently substituted with 0, 1, 2, 3, 4, or 5 R^(dd) groups, and wherein R^(aa), R^(bb), R^(cc) and R^(dd) are as defined herein. Nitrogen protecting groups are well known in the art and include those described in detail in Protecting Groups in Organic Synthesis, T. W. Greene and P. G. M. Wuts, 3^(rd) edition, John Wiley & Sons, 1999, incorporated herein by reference.

For example, nitrogen protecting groups such as amide groups (e.g., —C(═O)R^(aa)) include, but are not limited to, formamide, acetamide, chloroacetamide, trichloroacetamide, trifluoroacetamide, phenylacetamide, 3-phenylpropanamide, picolinamide, 3-pyridylcarboxamide, N-benzoylphenylalanyl derivative, benzamide, p-phenylbenzamide, o-nitophenylacetamide, o-nitrophenoxyacetamide, acetoacetamide, (N′-dithiobenzyloxyacylamino)acetamide, 3-(p-hydroxyphenyl)propanamide, 3-(o-nitrophenyl)propanamide, 2-methyl-2-(o-nitrophenoxy)propanamide, 2-methyl-2-(o-phenylazophenoxy)propanamide, 4-chlorobutanamide, 3-methyl-3-nitrobutanamide, o-nitrocinnamide, N-acetylmethionine derivative, o-nitrobenzamide and o-(benzoyloxymethyl)benzamide.

Nitrogen protecting groups such as carbamate groups (e.g., —C(═O)OR^(aa)) include, but are not limited to, methyl carbamate, ethyl carbamante, 9-fluorenylmethyl carbamate (Fmoc), 9-(2-sulfo)fluorenylmethyl carbamate, 9-(2,7-dibromo)fluoroenylmethyl carbamate, 2,7-di-t-butyl-[9-(10,10-dioxo-10,10,10,10-tetrahydrothioxanthyl)]methyl carbamate (DBD-Tmoc), 4-methoxyphenacyl carbamate (Phenoc), 2,2,2-trichloroethyl carbamate (Troc), 2-trimethylsilylethyl carbamate (Teoc), 2-phenylethyl carbamate (hZ), 1-(1-adamantyl)-1-methylethyl carbamate (Adpoc), 1,1-dimethyl-2-haloethyl carbamate, 1,1-dimethyl-2,2-dibromoethyl carbamate (DB-t-BOC), 1,1-dimethyl-2,2,2-trichloroethyl carbamate (TCBOC), 1-methyl-1-(4-biphenylyl)ethyl carbamate (Bpoc), 1-(3,5-di-t-butylphenyl)-1-methylethyl carbamate (t-Bumeoc), 2-(2′- and 4′-pyridyl)ethyl carbamate (Pyoc), 2-(N,N-dicyclohexylcarboxamido)ethyl carbamate, t-butyl carbamate (BOC), 1-adamantyl carbamate (Adoc), vinyl carbamate (Voc), allyl carbamate (Alloc), 1-isopropylallyl carbamate (Ipaoc), cinnamyl carbamate (Coc), 4-nitrocinnamyl carbamate (Noc), 8-quinolyl carbamate, N-hydroxypiperidinyl carbamate, alkyldithio carbamate, benzyl carbamate (Cbz), p-methoxybenzyl carbamate (Moz), p-nitobenzyl carbamate, p-bromobenzyl carbamate, p-chlorobenzyl carbamate, 2,4-dichlorobenzyl carbamate, 4-methylsulfinylbenzyl carbamate (Msz), 9-anthrylmethyl carbamate, diphenylmethyl carbamate, 2-methylthioethyl carbamate, 2-methylsulfonylethyl carbamate, 2-(p-toluenesulfonyl)ethyl carbamate, [2-(1,3-dithianyl)]methyl carbamate (Dmoc), 4-methylthiophenyl carbamate (Mtpc), 2,4-dimethylthiophenyl carbamate (Bmpc), 2-phosphonioethyl carbamate (Peoc), 2-triphenylphosphonioisopropyl carbamate (Ppoc), 1,1-dimethyl-2-cyanoethyl carbamate, m-chloro-p-acyloxybenzyl carbamate, p-(dihydroxyboryl)benzyl carbamate, 5-benzisoxazolylmethyl carbamate, 2-(trifluoromethyl)-6-chromonylmethyl carbamate (Tcroc), m-nitrophenyl carbamate, 3,5-dimethoxybenzyl carbamate, o-nitrobenzyl carbamate, 3,4-dimethoxy-6-nitrobenzyl carbamate, phenyl(o-nitrophenyl)methyl carbamate, t-amyl carbamate, S-benzyl thiocarbamate, p-cyanobenzyl carbamate, cyclobutyl carbamate, cyclohexyl carbamate, cyclopentyl carbamate, cyclopropylmethyl carbamate, p-decyloxybenzyl carbamate, 2,2-dimethoxyacylvinyl carbamate, o-(N,N-dimethylcarboxamido)benzyl carbamate, 1,1-dimethyl-3-(N,N-dimethylcarboxamido)propyl carbamate, 1,1-dimethylpropynyl carbamate, di(2-pyridyl)methyl carbamate, 2-furanylmethyl carbamate, 2-iodoethyl carbamate, isoborynl carbamate, isobutyl carbamate, isonicotinyl carbamate, p-(p′-methoxyphenylazo)benzyl carbamate, 1-methylcyclobutyl carbamate, 1-methylcyclohexyl carbamate, 1-methyl-1-cyclopropylmethyl carbamate, 1-methyl-1-(3,5-dimethoxyphenyl)ethyl carbamate, 1-methyl-1-(p-phenylazophenyl)ethyl carbamate, 1-methyl-1-phenylethyl carbamate, 1-methyl-1-(4-pyridyl)ethyl carbamate, phenyl carbamate, p-(phenylazo)benzyl carbamate, 2,4,6-tri-t-butylphenyl carbamate, 4-(trimethylammonium)benzyl carbamate, and 2,4,6-trimethylbenzyl carbamate.

Nitrogen protecting groups such as sulfonamide groups (e.g., —S(═O)₂R^(aa)) include, but are not limited to, p-toluenesulfonamide (Ts), benzenesulfonamide, 2,3,6,-trimethyl-4-methoxybenzenesulfonamide (Mtr), 2,4,6-trimethoxybenzenesulfonamide (Mtb), 2,6-dimethyl-4-methoxybenzenesulfonamide (Pme), 2,3,5,6-tetramethyl-4-methoxybenzenesulfonamide (Mte), 4-methoxybenzenesulfonamide (Mbs), 2,4,6-trimethylbenzenesulfonamide (Mts), 2,6-dimethoxy-4-methylbenzenesulfonamide (iMds), 2,2,5,7,8-pentamethylchroman-6-sulfonamide (Pmc), methanesulfonamide (Ms), β-trimethylsilylethanesulfonamide (SES), 9-anthracenesulfonamide, 4-(4′,8′-dimethoxynaphthylmethyl)benzenesulfonamide (DNMBS), benzylsulfonamide, trifluoromethylsulfonamide, and phenacylsulfonamide.

Other nitrogen protecting groups include, but are not limited to, phenothiazinyl-(10)-acyl derivative, N′-p-toluenesulfonylaminoacyl derivative, N′-phenylaminothioacyl derivative, N-benzoylphenylalanyl derivative, N-acetylmethionine derivative, 4,5-diphenyl-3-oxazolin-2-one, N-phthalimide, N-dithiasuccinimide (Dts), N-2,3-diphenylmaleimide, N-2,5-dimethylpyrrole, N-1,1,4,4-tetramethyldisilylazacyclopentane adduct (STABASE), 5-substituted 1,3-dimethyl-1,3,5-triazacyclohexan-2-one, 5-substituted 1,3-dibenzyl-1,3,5-triazacyclohexan-2-one, 1-substituted 3,5-dinitro-4-pyridone, N-methylamine, N-allylamine, N-[2-(trimethylsilyl)ethoxy]methylamine (SEM), N-3-acetoxypropylamine, N-(1-isopropyl-4-nitro-2-oxo-3-pyroolin-3-yl)amine, quaternary ammonium salts, N-benzylamine, N-di(4-methoxyphenyl)methylamine, N-5-dibenzosuberylamine, N-triphenylmethylamine (Tr), N-[(4-methoxyphenyl)diphenylmethyl]amine (MMTr), N-9-phenylfluorenylamine (PhF), N-2,7-dichloro-9-fluorenylmethyleneamine, N-ferrocenylmethylamino (Fcm), N-2-picolylamino N′-oxide, N-1,1-dimethylthiomethyleneamine, N-benzylideneamine, N-p-methoxybenzylideneamine, N-diphenylmethyleneamine, N-[(2-pyridyl)mesityl]methyleneamine, N—(N′,N′-dimethylaminomethylene)amine, N,N′-isopropylidenediamine, N-p-nitrobenzylideneamine, N-salicylideneamine, N-5-chlorosalicylideneamine, N-(5-chloro-2-hydroxyphenyl)phenylmethyleneamine, N-cyclohexylideneamine, N-(5,5-dimethyl-3-oxo-1-cyclohexenyl)amine, N-borane derivative, N-diphenylborinic acid derivative, N-[phenyl(pentaacylchromium- or tungsten)acyl]amine, N-copper chelate, N-zinc chelate, N-nitroamine, N-nitrosoamine, amine N-oxide, diphenylphosphinamide (Dpp), dimethylthiophosphinamide (Mpt), diphenylthiophosphinamide (Ppt), dialkyl phosphoramidates, dibenzyl phosphoramidate, diphenyl phosphoramidate, benzenesulfenamide, o-nitrobenzenesulfenamide (Nps), 2,4-dinitrobenzenesulfenamide, pentachlorobenzenesulfenamide, 2-nitro-4-methoxybenzenesulfenamide, triphenylmethylsulfenamide, and 3-nitropyridinesulfenamide (Npys).

In certain embodiments, the substituent present on an oxygen atom is an oxygen protecting group (also referred to herein as an “hydroxyl protecting group”). Oxygen protecting groups include, but are not limited to, —R^(aa), —N(R^(bb))₂, —C(═O)SR^(aa), —C(═O)R^(aa), —CO₂R^(aa), —C(═O)N(R^(bb))₂, —C(═NR^(bb))R^(aa), —C(═NR^(bb))OR^(aa), —C(═NR^(bb))N(R^(bb))₂, —S(═O)R^(aa), —SO₂R^(aa), —Si(R^(aa))₃, —P(R^(cc))₂, —P(R^(cc))₃, —P(═O)₂R^(aa), —P(═O)(R^(aa))₂, —P(═O)(OR^(cc))₂, —P(═O)₂N(R^(bb))₂, and —P(═O)(NR^(bb))₂, wherein R^(aa), R^(bb), and R^(cc) are as defined herein. Oxygen protecting groups are well known in the art and include those described in detail in Protecting Groups in Organic Synthesis, T. W. Greene and P. G. M. Wuts, 3^(rd) edition, John Wiley & Sons, 1999, incorporated herein by reference.

Exemplary oxygen protecting groups include, but are not limited to, methyl, methoxylmethyl (MOM), methylthiomethyl (MTM), t-butylthiomethyl, (phenyldimethylsilyl)methoxymethyl (SMOM), benzyloxymethyl (BOM), p-methoxybenzyloxymethyl (PMBM), (4-methoxyphenoxy)methyl (p-AOM), guaiacolmethyl (GUM), t-butoxymethyl, 4-pentenyloxymethyl (POM), siloxymethyl, 2-methoxyethoxymethyl (MEM), 2,2,2-trichloroethoxymethyl, bis(2-chloroethoxy)methyl, 2-(trimethylsilyl)ethoxymethyl (SEMOR), tetrahydropyranyl (THP), 3-bromotetrahydropyranyl, tetrahydrothiopyranyl, 1-methoxycyclohexyl, 4-methoxytetrahydropyranyl (MTHP), 4-methoxytetrahydrothiopyranyl, 4-methoxytetrahydrothiopyranyl S,S-dioxide, 1-[(2-chloro-4-methyl)phenyl]-4-methoxypiperidin-4-yl (CTMP), 1,4-dioxan-2-yl, tetrahydrofuranyl, tetrahydrothiofuranyl, 2,3,3a,4,5,6,7,7a-octahydro-7,8,8-trimethyl-4,7-methanobenzofuran-2-yl, 1-ethoxyethyl, 1-(2-chloroethoxyl)ethyl, 1-methyl-1-methoxyethyl, 1-methyl-1-benzyloxyethyl, 1-methyl-1-benzyloxy-2-fluoroethyl, 2,2,2-trichloroethyl, 2-trimethylsilylethyl, 2-(phenylselenyl)ethyl, t-butyl, allyl, p-chlorophenyl, p-methoxyphenyl, 2,4-dinitrophenyl, benzyl (Bn), p-methoxybenzyl, 3,4-dimethoxybenzyl, o-nitrobenzyl, p-nitrobenzyl, p-halobenzyl, 2,6-dichlorobenzyl, p-cyanobenzyl, p-phenylbenzyl, 2-picolyl, 4-picolyl, 3-methyl-2-picolyl N-oxido, diphenylmethyl, p,p′-dinitrobenzhydryl, 5-dibenzosuberyl, triphenylmethyl, a-naphthyldiphenylmethyl, p-methoxyphenyldiphenylmethyl, di(p-methoxyphenyl)phenylmethyl, tri(p-methoxyphenyl)methyl, 4-(4′-bromophenacyloxyphenyl)diphenylmethyl, 4,4′,4″-tris(4,5-dichlorophthalimidophenyl)methyl, 4,4′,4″-tris(levulinoyloxyphenyl)methyl, 4,4′,4″-tris(benzoyloxyphenyl)methyl, 3-(imidazol-1-yl)bis(4′,4′-dimethoxyphenyl)methyl, 1,1-bis(4-methoxyphenyl)-1′-pyrenylmethyl, 9-anthryl, 9-(9-phenyl)xanthenyl, 9-(9-phenyl-10-oxo)anthryl, 1,3-benzodithiolan-2-yl, benzisothiazolyl S,S-dioxido, trimethylsilyl (TMS), triethylsilyl (TES), triisopropylsilyl (TIPS), dimethylisopropylsilyl (IPDMS), diethylisopropylsilyl (DEIPS), dimethylthexylsilyl, t-butyldimethylsilyl (TBDMS), t-butyldiphenylsilyl (TBDPS), tribenzylsilyl, tri-p-xylylsilyl, triphenylsilyl, diphenylmethylsilyl (DPMS), t-butylmethoxyphenylsilyl (TBMPS), formate, benzoylformate, acetate, chloroacetate, dichloroacetate, trichloroacetate, trifluoroacetate, methoxyacetate, triphenylmethoxyacetate, phenoxyacetate, p-chlorophenoxyacetate, 3-phenylpropionate, 4-oxopentanoate (levulinate), 4,4-(ethylenedithio)pentanoate (levulinoyldithioacetal), pivaloate, adamantoate, crotonate, 4-methoxycrotonate, benzoate, p-phenylbenzoate, 2,4,6-trimethylbenzoate (mesitoate), methyl carbonate, 9-fluorenylmethyl carbonate (Fmoc), ethyl carbonate, 2,2,2-trichloroethyl carbonate (Troc), 2-(trimethylsilyl)ethyl carbonate (TMSEC), 2-(phenylsulfonyl) ethyl carbonate (Psec), 2-(triphenylphosphonio) ethyl carbonate (Peoc), isobutyl carbonate, vinyl carbonate, allyl carbonate, t-butyl carbonate (BOC), p-nitrophenyl carbonate, benzyl carbonate, p-methoxybenzyl carbonate, 3,4-dimethoxybenzyl carbonate, o-nitrobenzyl carbonate, p-nitrobenzyl carbonate, S-benzyl thiocarbonate, 4-ethoxy-1-napththyl carbonate, methyl dithiocarbonate, 2-iodobenzoate, 4-azidobutyrate, 4-nitro-4-methylpentanoate, o-(dibromomethyl)benzoate, 2-formylbenzenesulfonate, 2-(methylthiomethoxy)ethyl, 4-(methylthiomethoxy)butyrate, 2-(methylthiomethoxymethyl)benzoate, 2,6-dichloro-4-methylphenoxyacetate, 2,6-dichloro-4-(1,1,3,3-tetramethylbutyl)phenoxyacetate, 2,4-bis(1,1-dimethylpropyl)phenoxyacetate, chlorodiphenylacetate, isobutyrate, monosuccinoate, (E)-2-methyl-2-butenoate, o-(methoxyacyl)benzoate, α-naphthoate, nitrate, alkyl N,N,N′,N′-tetramethylphosphorodiamidate, alkyl N-phenylcarbamate, borate, dimethylphosphinothioyl, alkyl 2,4-dinitrophenylsulfenate, sulfate, methanesulfonate (mesylate), benzylsulfonate, and tosylate (Ts).

In certain embodiments, the substituent present on an sulfur atom is a sulfur protecting group (also referred to as a “thiol protecting group”). Sulfur protecting groups include, but are not limited to, —R^(aa), —N(R^(bb))₂, —C(═O)SR^(aa), —C(═O)R^(aa), —CO₂R^(aa), —C(═O)N(R^(bb))₂, —C(═NR^(bb))R^(aa), —C(═NR^(bb))OR^(aa), —C(═NR^(bb))N(R^(bb))₂, —S(═O)R^(aa), —SO₂R^(aa), —Si(R^(aa))₃, —P(R^(cc))₂, —P(R^(cc))₃, —P(═O)₂R^(aa), —P(═O)(R^(aa))₂, —P(═O)(OR^(cc))₂, —P(═O)₂N(R^(bb))₂, and —P(═O)(NR^(bb))₂, wherein R^(aa), R^(bb), and R^(cc) are as defined herein. Sulfur protecting groups are well known in the art and include those described in detail in Protecting Groups in Organic Synthesis, T. W. Greene and P. G. M. Wuts, 3^(rd) edition, John Wiley & Sons, 1999, incorporated herein by reference.

As used herein, when two entities are “conjugated” or “ligated” to one another, they are linked by a direct or indirect covalent or non-covalent interaction. In certain embodiments, the association is covalent. In other embodiments, the association is non-covalent. Non-covalent interactions include hydrogen bonding, van der Waals interactions, hydrophobic interactions, magnetic interactions, electrostatic interactions, etc. In certain embodiments, two entities are covalently connected, optionally through a linker group.

As used herein, the term “salt” refers to any and all salts, including pharmaceutically acceptable salt which refers to those salts within the scope of sound medical judgment, suitable for use in contact with the tissues of humans and lower animals without undue toxicity, irritation, allergic response and the like, and are commensurate with a reasonable benefit/risk ratio (see Berge et al. describes pharmaceutically acceptable salts in detail in J. Pharmaceutical Sciences (1977) 66:1-19). Examples of pharmaceutically acceptable, nontoxic acid salts are salts of an amino group formed with inorganic acids such as hydrochloric acid, hydrobromic acid, phosphoric acid, sulfuric acid and perchloric acid or with organic acids such as acetic acid, oxalic acid, maleic acid, tartaric acid, citric acid, succinic acid, or malonic acid or by using other methods used in the art such as ion exchange. Other pharmaceutically acceptable salts include adipate, alginate, ascorbate, aspartate, benzenesulfonate, benzoate, bisulfate, borate, butyrate, camphorate, camphorsulfonate, citrate, cyclopentanepropionate, digluconate, dodecylsulfate, ethanesulfonate, formate, fumarate, glucoheptonate, glycerophosphate, gluconate, hemisulfate, heptanoate, hexanoate, hydroiodide, 2-hydroxy-ethanesulfonate, lactobionate, lactate, laurate, lauryl sulfate, malate, maleate, malonate, methanesulfonate, 2-naphthalenesulfonate, nicotinate, nitrate, oleate, oxalate, palmitate, pamoate, pectinate, persulfate, 3-phenylpropionate, phosphate, picrate, pivalate, propionate, stearate, succinate, sulfate, tartrate, thiocyanate, p-toluenesulfonate, undecanoate, valerate salts, and the like. Pharmaceutically acceptable salts derived from appropriate bases include alkali metal, alkaline earth metal, ammonium and N⁺(C₁₋₄alkyl)₄ salts. Representative alkali or alkaline earth metal salts include sodium, lithium, potassium, calcium, magnesium, and the like. Further pharmaceutically acceptable salts include, when appropriate, nontoxic ammonium, quaternary ammonium, and amine cations formed using counterions such as halide, hydroxide, carboxylate, sulfate, phosphate, nitrate, lower alkyl sulfonate, and aryl sulfonate.

A “subject” to which administration is contemplated includes, but is not limited to, humans (i.e., a male or female of any age group, e.g., a pediatric subject (e.g., infant, child, adolescent) or adult subject (e.g., young adult, middle-aged adult, or senior adult)) and/or other non-human animals, for example, mammals (e.g., primates (e.g., cynomolgus monkeys, rhesus monkeys); commercially relevant mammals such as cattle, pigs, horses, sheep, goats, cats, and/or dogs) and birds (e.g., commercially relevant birds such as chickens, ducks, geese, and/or turkeys). In certain embodiments, the animal is a mammal. The animal may be a male or female and at any stage of development. A non-human animal may be a transgenic animal.

As used herein, the terms “condition,” “disease,” and “disorder” are used interchangeably.

As used herein “inhibition”, “inhibiting”, “inhibit” and “inhibitor”, and the like, refer to the ability of a compound to reduce, slow, halt, or prevent the activity of a particular biological process.

As used herein, the term “cell” present disclosure is meant to encompass eukaryotic and prokaryotic cells of any genus or species, with mammalian cells being of particular interest. “Cell” is also meant to encompass both normal cells and diseased cells, e.g., cancerous cells. In certain embodiments, the cells described herein are living cells.

As used herein the term “sample” includes any chemical sample or biological sample. Chemical sample refers to any chemical mixtures or chemical compounds. Biological sample includes, without limitation, cell cultures or extracts thereof; biopsied material obtained from an animal (e.g., mammal) or extracts thereof; and blood, saliva, urine, feces, semen, tears, or other body fluids or extracts thereof. For example, the term “biological sample” refers to any solid or fluid sample obtained from, excreted by or secreted by any living organism, including single-celled microorganisms (such as bacteria and yeasts) and multicellular organisms (such as plants and animals, for instance a vertebrate or a mammal, and in particular a healthy or apparently healthy human subject or a human patient affected by a condition or disease to be diagnosed or investigated). The biological sample can be in any form, including a solid material such as a tissue, cells, a cell pellet, a cell extract, cell homogenates, or cell fractions; or a biopsy, or a biological fluid. The biological fluid may be obtained from any site (e.g. blood, saliva (or a mouth wash containing buccal cells), tears, plasma, serum, urine, bile, cerebrospinal fluid, amniotic fluid, peritoneal fluid, and pleural fluid, or cells therefrom, aqueous or vitreous humor, or any bodily secretion), a transudate, an exudate (e.g. fluid obtained from an abscess or any other site of infection or inflammation), or fluid obtained from a joint (e.g. a normal joint or a joint affected by disease such as rheumatoid arthritis, osteoarthritis, gout or septic arthritis). The biological sample can be obtained from any organ or tissue (including a biopsy or autopsy specimen) or may comprise cells (whether primary cells or cultured cells) or medium conditioned by any cell, tissue or organ. Biological samples may also include sections of tissues such as frozen sections taken for histological purposes. Biological samples also include mixtures of biological molecules including proteins, lipids, carbohydrates and nucleic acids generated by partial or complete fractionation of cell or tissue homogenates. Although the sample is preferably taken from a human subject, biological samples may be from any animal, plant, bacteria, virus, yeast, etc. The term animal, as used herein, refers to humans as well as non-human animals, at any stage of development, including, for example, mammals, birds, reptiles, amphibians, fish, worms and single cells. Cell cultures and live tissue samples are considered to be pluralities of animals. In certain exemplary embodiments, the non-human animal is a mammal (e.g., a rodent, a mouse, a rat, a rabbit, a monkey, a dog, a cat, a sheep, cattle, a primate, or a pig). An animal may be a transgenic animal or a human clone. If desired, the biological sample may be subjected to preliminary processing, including preliminary separation techniques.

The term “physiological conditions” is meant to encompass those conditions compatible with living cells, e.g., predominantly aqueous conditions of a temperature, pH, salinity, etc. that are compatible with living cells.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a fluorogenic CuAAC reaction.

FIG. 2 shows an exemplary synthesis scheme of Compound 1.

FIG. 3 is a diagram showing the reaction between Compound 1 and benzyl azide. (3 a) Time course of normalized fluorescence intensity in the SPAAC reaction of Compound 1 with benzyl azide. (3 b) Plot of 1/[compound 1] vs. time for the reaction of Compound 1 and benzyl azide in CD₃CN as monitored by ¹H-NMR. The measurement was repeated 3 times with a concentration of 19 mM.

FIG. 4 shows an exemplary synthetic scheme of compound C, a green-emitting coumarin having an alkyne group.

FIG. 5 shows exemplary synthetic schemes Compounds 1-A and 1-B.

FIG. 6 is a table showing the spectroscopic properties of Compound 1 and compounds 1-A and 1-B.

FIG. 7 shows the (7 a) absorption and Fluorescence emission spectra (λ_(ex)=330 nm) of Compounds 1, 1-A, and 1-B (45 μM, PBS buffer containing 10% DMSO, pH 7.4, 37° C.) (8 a) and the time course of normalized fluorescence intensity at 435 nm (λ_(ex)=330 nm) for the ligation reaction of 1 with N-azidoacetylmannosamine in PBS buffer containing 10% DMSO at 37° C. (7 b)

FIG. 8 is a photo showing the time-lapse fluorescence and overlaid images of living CL1-5 cells incubated with Ac4ManNAz and labeled with Compound 1 under no-wash and no-fixation conditions: fluorescence image of cells (upper row) and brightfield overlaid image of cells (bottom row). Control: cells incubated with Ac₄ManNAc. (Scale bar: 25 μm).

FIG. 9 is a photo showing the localization of probe-labeled sialyl glycoconjugates in CL1-5 cells as visualized by confocal microscopy. Cells incubated with 200 μM of Ac₄ManNAz were labeled with 100 μM of Compound 1 and stained with fluorescein-conjugated WGA lectin (for Golgi) and propidium iodide (for nucleus).

FIG. 10 is a plot of 1/[1] vs. time for the reaction of Compound 1 and N-azidoacetylmannosamine in a solution of CD₃OD-D₂O (5:1, v/v) as monitored by ¹H-NMR. The reaction was monitored by ¹H-NMR.

FIG. 11 shows the absorption (11 a) and fluorescence emission (11 b) spectra (λ_(ex)=330 nm) of Compounds 1, 1-A and 1-B (45 μM, 10% DMSO in PBS buffer, pH 7.4, 37° C.).

FIG. 12 is a photo showing the time-lapse fluorescence and overlaid images of living CL1-5 cells incubated with Ac₄ManNAz and labeled with Compound 1 under no-wash and no-fixation conditions: fluorescence image of cells (upper row) and brightfield overlaid image of cells (bottom row). Control: cells incubated with Ac₄ManNAc. (Scale bar: 10 μm).

DETAILED DESCRIPTION OF THE PRESENT DISCLOSURE

The present disclosure provides novel benzocyclooctyne compounds of formula (I). These compounds undergo strain-promoted azide-alkyne cycloadditions (SPAAC) without presence of toxic metal catalyst. Exemplary coumarin-cyclooctyne compounds according to the present disclosure react with azide compounds to give the triazole products with enhanced fluorescence to facilitate the detection in a target molecule. The provided compounds represent a significant advance in live-cell imaging, and are applicable to real-time detection of biochemical events in vivo.

In one aspect, the present disclosure provides a compound of Formula (I):

-   -   or a salt thereof,     -   wherein     -   X₁, X₂, X₃, and X₄ are in a 8-membered carbocycle or         heterocycle; provided that when the 8-membered ring is a         heterocycle, three of X₁, X₂, X₃, and X₄ are carbon atoms, and         one of X₁, X₂, X₃, and X₄ is N, O, P, or S;     -   each of G¹, G², G³ and G⁴ is independently selected from         hydrogen, halogen, optionally substituted C₁-C₆ alkyl,         optionally substituted alkenyl, optionally substituted alkynyl,         optionally substituted heterocyclyl, optionally substituted         aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A),         —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C),         —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C),         —SO₂R^(A), —SO₂N(R^(B))₂, ═O, ═NOH, ═N—OR^(A), ═N—NH₂,         ═N—NHR^(B), ═N—N(R^(B))₂, and —NHSO₂R^(A); or G¹ and G² are         taken together with their intervening atoms to form an         optionally substituted carbocycle or heterocycle; or G³ and G⁴         are taken together with their intervening atoms to form an         optionally substituted carbocycle or heterocycle;     -   each of G⁵ and G⁸ is independently selected from hydrogen,         halogen, optionally substituted C₁-C₆ alkyl, optionally         substituted alkenyl, optionally substituted alkynyl, optionally         substituted heterocyclyl, optionally substituted aryl,         optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A),         —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C),         —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C),         —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A);     -   each of G⁶ and G⁷ is independently selected from hydrogen,         halogen, optionally substituted C₁-C₆ alkyl, optionally         substituted alkenyl, optionally substituted alkynyl, optionally         substituted heterocyclyl, optionally substituted aryl,         optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A),         —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C),         —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C),         —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A), or G⁶ and G⁷ are         taken together with their intervening atoms to form an         optionally substituted carbocycle or heterocycle;     -   each instance of R^(A) is independently hydrogen, optionally         substituted C₁-C₆ alkyl, optionally substituted alkenyl,         optionally substituted alkynyl, optionally substituted         heterocyclyl, optionally substituted aryl, optionally         substituted heteroaryl, or an oxygen protecting group when         attached to an oxygen, or a sulfur protecting group when         attached to sulfur; and     -   each instance of R^(B) is independently hydrogen, optionally         substituted C₁-C₆ alkyl, optionally substituted alkenyl,         optionally substituted alkynyl, optionally substituted         heterocyclyl, optionally substituted aryl, optionally         substituted heteroaryl, or a nitrogen protecting group, or two         R^(B) taken together with the intervening nitrogen form a         heterocycle;     -   each instance of R^(C) is independently hydrogen, optionally         substituted C₁-C₆ alkyl, optionally substituted alkenyl,         optionally substituted alkynyl, optionally substituted         heterocyclyl, optionally substituted aryl, or optionally         substituted heteroaryl; and     -   provided that when G¹ and G² are taken together with their         intervening atoms to form an optionally substituted phenyl, G⁶         and G⁷ are taken together with their intervening atoms to form         an optionally substituted heterocycle and X⁴ is not N.

For the compounds of formula (I), when G¹ and G² are taken together with their intervening atoms to form an optionally substituted phenyl, G⁶ and G⁷ are taken together with their intervening atoms to form an optionally substituted heterocycle and X⁴ is not N.

As generally defined herein, X₁, X₂, X₃, and X₄ are in a 8-membered carbocycle or heterocycle; provided that when the 8-membered ring is a heterocycle, three of X₁, X₂, X₃, and X₄ are carbon atoms, and one of X₁, X₂, X₃, and X₄ is N, O, P, or S. In certain embodiments, X₁, X₂, X₃, and X₄ are in a 8-membered carbocycle. In certain embodiments, X₁, X₂, X₃, and X₄ are in a 8-membered heterocycle. In certain embodiments, X₁, X₂, and X₃ are carbon atoms, and X₄ is N, O, P, or S. In certain embodiments, X₁, X₂, and X₄ are carbon atoms, and X₃ is N, O, P, or S. In certain embodiments, X₁, X₃, and X₄ are carbon atoms, and X₂ is N, O, P, or S. In certain embodiments, X₂, X₃, and X₄ are carbon atoms, and X₁ is N, O, P, or S.

As generally defined herein, G¹ is independently selected from hydrogen, halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, ═O, ═NOH, ═N—OR^(A), ═N—NH₂, ═N—NHR^(B), ═N—N(R^(B))₂, and —NHSO₂R^(A). In certain embodiments, G¹ is H. In certain embodiments, G¹ is halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, ═O, ═NOH, ═N—OR^(A), ═N—NH₂, ═N—NHR^(B), ═N—N(R^(B))₂, and —NHSO₂R^(A). In certain embodiments, G¹ is halogen. In certain embodiments, G¹ is optionally substituted C₁-C₆ alkyl. In certain embodiments, G¹ is methyl, ethyl, or n-propyl. In certain embodiments, G¹ is —OR^(A), wherein R^(A) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, or an oxygen protecting group when attached to an oxygen, or a sulfur protecting group when attaching to sulfur. In certain embodiments, G¹ is —OH. In certain embodiments, G¹ is —OR^(A), wherein R^(A) is optionally substituted C₁-C₆ alkyl. In certain embodiments, G¹ is —OCH₃ or —OC₂H₅. In certain embodiments, G¹ is —OR^(A), wherein R^(A) is an oxygen protecting group. In certain embodiments, G¹ is —N(R^(B))₂, wherein each instance of R^(B) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, and optionally substituted aryl, or a nitrogen protecting group, or two R^(B) taken together with the intervening nitrogen form a heterocycle. In certain embodiments, G¹ is NH₂. In certain embodiments, G¹ is NHR^(B), wherein R^(B) is optionally substituted C₁-C₆ alkyl. In certain embodiments, G¹ is NHCH₃ or NHC₂H₅. In certain embodiments, G¹ is NHR^(B), wherein R^(B) is a nitrogen protecting group.

As generally defined herein, G² is independently selected from hydrogen, halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, ═O, ═NOH, ═N—OR^(A), ═N—NH₂, ═N—NHR^(B), ═N—N(R^(B))₂, and —NHSO₂R^(A). In certain embodiments, G² is H. In certain embodiments, G² is halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, ═O, ═NOH, ═N—OR^(A), ═N—NH₂, ═N—NHR^(B), ═N—N(R^(B))₂, and —NHSO₂R^(A). In certain embodiments, G² is halogen. In certain embodiments, G² is optionally substituted C₁-C₆ alkyl. In certain embodiments, G² is methyl, ethyl, or n-propyl. In certain embodiments, G⁷ is —OR^(A), wherein R^(A) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, or an oxygen protecting group when attached to an oxygen, or a sulfur protecting group when attaching to sulfur. In certain embodiments, G² is —OH. In certain embodiments, G² is —OR^(A), wherein R^(A) is optionally substituted C₁-C₆ alkyl. In certain embodiments, G² is —OCH₃ or —OC₂H₅. In certain embodiments, G² is —OR^(A), wherein R^(A) is an oxygen protecting group. In certain embodiments, G² is —N(R^(B))₂, wherein each instance of R^(B) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, and optionally substituted aryl, or a nitrogen protecting group, or two R^(B) taken together with the intervening nitrogen form a heterocycle. In certain embodiments, G² is NH₂. In certain embodiments, G² is NHR^(B), wherein R^(B) is optionally substituted C₁-C₆ alkyl. In certain embodiments, G² is NHCH₃ or NHC₂H₅. In certain embodiments, G² is NHR^(B), wherein R^(B) is a nitrogen protecting group.

As generally defined herein, G³ is independently selected from hydrogen, halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, ═O, ═NOH, ═N—OR^(A), ═N—NH₂, ═N—NHR^(B), ═N—N(R^(B))₂, and —NHSO₂R^(A). In certain embodiments, G³ is H. In certain embodiments, G³ is halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, ═O, ═NOH, ═N—OR^(A), ═N—NH₂, ═N—NHR^(B), ═N—N(R^(B))₂, and —NHSO₂R^(A). In certain embodiments, G³ is halogen. In certain embodiments, G³ is optionally substituted C₁-C₆ alkyl. In certain embodiments, G³ is methyl, ethyl, or n-propyl. In certain embodiments, G⁷ is —OR^(A), wherein R^(A) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, or an oxygen protecting group when attached to an oxygen, or a sulfur protecting group when attaching to sulfur. In certain embodiments, G³ is —OH. In certain embodiments, G³ is —OR^(A), wherein R^(A) is optionally substituted C₁-C₆ alkyl. In certain embodiments, G³ is —OCH₃ or —OC₂H₅. In certain embodiments, G³ is —OR^(A), wherein R^(A) is an oxygen protecting group. In certain embodiments, G³ is —N(R^(B))₂, wherein each instance of R^(B) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, and optionally substituted aryl, or a nitrogen protecting group, or two R^(B) taken together with the intervening nitrogen form a heterocycle. In certain embodiments, G³ is NH₂. In certain embodiments, G³ is NHR^(B), wherein R^(B) is optionally substituted C₁-C₆ alkyl. In certain embodiments, G³ is NHCH₃ or NHC₂H₅. In certain embodiments, G³ is NHR^(B), wherein R^(B) is a nitrogen protecting group.

As generally defined herein, G⁴ is independently selected from hydrogen, halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, ═O, ═NOH, ═N—OR^(A), ═N—NH₂, ═N—NHR^(B), ═N—N(R^(B))₂, and —NHSO₂R^(A). In certain embodiments, G⁴ is H. In certain embodiments, G⁴ is halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, ═O, ═NOH, ═N—OR^(A), ═N—NH₂, ═N—NHR^(B), ═N—N(R^(B))₂, and —NHSO₂R^(A). In certain embodiments, G⁴ is halogen. In certain embodiments, G⁴ is optionally substituted C₁-C₆ alkyl. In certain embodiments, G⁴ is methyl, ethyl, or n-propyl. In certain embodiments, G⁴ is —OR^(A), wherein R^(A) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, or an oxygen protecting group when attached to an oxygen, or a sulfur protecting group when attaching to sulfur. In certain embodiments, G⁴ is —OH. In certain embodiments, G⁴ is —OR^(A), wherein R^(A) is optionally substituted C₁-C₆ alkyl. In certain embodiments, G⁴ is —OCH₃ or —OC₂H₅. In certain embodiments, G⁴ is —OR^(A), wherein R^(A) is an oxygen protecting group. In certain embodiments, G⁴ is —N(R^(B))₂, wherein each instance of R^(B) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, and optionally substituted aryl, or a nitrogen protecting group, or two R^(B) taken together with the intervening nitrogen form a heterocycle. In certain embodiments, G⁴ is NH₂. In certain embodiments, G⁴ is NHR^(B), wherein R^(B) is optionally substituted C₁-C₆ alkyl. In certain embodiments, G⁴ is NHCH₃ or NHC₂H₅. In certain embodiments, G⁴ is NHR^(B), wherein R^(B) is a nitrogen protecting group.

In certain embodiments, G¹ and G² are taken together with their intervening atoms to form an optionally substituted carbocycle or heterocycle. In certain embodiments, G¹ and G² are taken together with their intervening atoms to form an optionally substituted carbocycle. In certain embodiments, G¹ and G² are taken together with their intervening atoms to form an optionally substituted 5-membered carbocycle. In certain embodiments, G¹ and G² are taken together with their intervening atoms to form an optionally substituted 6-membered carbocycle. In certain embodiments, G¹ and G² are taken together with their intervening atoms to form an optionally substituted phenyl. In certain embodiments, G¹ and G² are taken together with their intervening atoms to form an unsubstituted phenyl. In certain embodiments, G¹ and G² are taken together with their intervening atoms to form an optionally substituted heterocycle. In certain embodiments, G¹ and G² are taken together with their intervening atoms to form an optionally substituted 5-membered heterocycle with one heteroatom of S, N, or O. In certain embodiments, G¹ and G² are taken together with their intervening atoms to form an optionally substituted 5-membered heterocycle with two heteroatom each independently selected from the group of S, N, and O. In certain embodiments, G¹ and G² are taken together with their intervening atoms to form an optionally substituted 6-membered carbocycle with one heteroatom of S, N, or O. In certain embodiments, G¹ and G² are taken together with their intervening atoms to form an optionally substituted 6-membered carbocycle with two heteroatoms each independently selected from the group consisting of S, N, and O.

In certain embodiments, G³ and G⁴ are taken together with their intervening atoms to form an optionally substituted carbocycle or heterocycle. In certain embodiments, G³ and G⁴ are taken together with their intervening atoms to form an optionally substituted carbocycle. In certain embodiments, G³ and G⁴ are taken together with their intervening atoms to form an optionally substituted cyclopropyl. In certain embodiments, G³ and G⁴ are taken together with their intervening atoms to form an optionally substituted 4-membered carbocycle. In certain embodiments, G³ and G⁴ are taken together with their intervening atoms to form an optionally substituted 5-membered carbocycle. In certain embodiments, G³ and G⁴ are taken together with their intervening atoms to form an optionally substituted 6-membered carbocycle. In certain embodiments, G³ and G⁴ are taken together with their intervening atoms to form an optionally substituted heterocycle. In certain embodiments, G³ and G⁴ are taken together with their intervening atoms to form an optionally substituted 5-membered heterocycle with one heteroatom of S, N, or O. In certain embodiments, G³ and G⁴ are taken together with their intervening atoms to form an optionally substituted 5-membered heterocycle with two heteroatom each independently selected from the group of S, N, and O. In certain embodiments, G³ and G⁴ are taken together with their intervening atoms to form an optionally substituted 6-membered carbocycle with one heteroatom of S, N, or O. In certain embodiments, G³ and G⁴ are taken together with their intervening atoms to form an optionally substituted 6-membered carbocycle with two heteroatoms each independently selected from the group consisting of S, N, and O.

As generally defined herein, G⁵ is independently selected from hydrogen, halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A). In certain embodiments, G⁵ is H. In certain embodiments, G⁵ is halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A). In certain embodiments, G⁵ is halogen. In certain embodiments, G⁵ is optionally substituted C₁-C₆ alkyl. In certain embodiments, G⁵ is methyl, ethyl, or n-propyl. In certain embodiments, G⁵ is —OR^(A), wherein R^(A) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, or an oxygen protecting group when attached to an oxygen, or a sulfur protecting group when attaching to sulfur. In certain embodiments, G⁵ is —OH. In certain embodiments, G⁵ is —OR^(A), wherein R^(A) is optionally substituted C₁-C₆ alkyl. In certain embodiments, G⁵ is —OCH₃ or —OC₂H₅. In certain embodiments, G⁵ is —OR^(A), wherein R^(A) is an oxygen protecting group. In certain embodiments, G⁵ is —N(R^(B))₂, wherein each instance of R^(B) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, and optionally substituted aryl, or a nitrogen protecting group, or two R^(B) taken together with the intervening nitrogen form a heterocycle. In certain embodiments, G⁵ is NH₂. In certain embodiments, G⁵ is NHR^(B), wherein R^(B) is optionally substituted C₁-C₆ alkyl. In certain embodiments, G⁵ is NHCH₃ or NHC₂H₅. In certain embodiments, G⁵ is NHR^(B), wherein R^(B) is a nitrogen protecting group.

As generally defined herein, G⁸ is independently selected from hydrogen, halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A). In certain embodiments, G⁸ is H. In certain embodiments, G⁸ is halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A). In certain embodiments, G⁸ is halogen. In certain embodiments, G⁸ is optionally substituted C₁-C₆ alkyl. In certain embodiments, G⁸ is methyl, ethyl, or n-propyl. In certain embodiments, G⁸ is —OR^(A), wherein R^(A) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, or an oxygen protecting group when attached to an oxygen, or a sulfur protecting group when attaching to sulfur. In certain embodiments, G⁸ is —OH. In certain embodiments, G⁸ is —OR^(A), wherein R^(A) is optionally substituted C₁-C₆ alkyl. In certain embodiments, G⁸ is —OCH₃ or —OC₂H₅. In certain embodiments, G⁸ is —OR^(A), wherein R^(A) is an oxygen protecting group. In certain embodiments, G⁸ is —N(R^(B))₂, wherein each instance of R^(B) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, and optionally substituted aryl, or a nitrogen protecting group, or two R^(B) taken together with the intervening nitrogen form a heterocycle. In certain embodiments, G⁸ is NH₂. In certain embodiments, G⁸ is NHR^(B), wherein R^(B) is optionally substituted C₁-C₆ alkyl. In certain embodiments, G⁸ is NHCH₃ or NHC₂H₅. In certain embodiments, G⁸ is NHR^(B), wherein R^(B) is a nitrogen protecting group.

As generally defined herein, G⁶ is independently selected from hydrogen, halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A). In certain embodiments, G⁶ is H. In certain embodiments, G⁶ is halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A). In certain embodiments, G⁶ is halogen. In certain embodiments, G⁶ is optionally substituted C₁-C₆ alkyl. In certain embodiments, G⁶ is methyl, ethyl, or n-propyl. In certain embodiments, G⁶ is —OR^(A), wherein R^(A) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, or an oxygen protecting group when attached to an oxygen, or a sulfur protecting group when attaching to sulfur. In certain embodiments, G⁶ is —OH. In certain embodiments, G⁶ is —OR^(A), wherein R^(A) is optionally substituted C₁-C₆ alkyl. In certain embodiments, G⁶ is —OCH₃ or —OC₂H₅. In certain embodiments, G⁶ is —OR^(A), wherein R^(A) is an oxygen protecting group. In certain embodiments, G⁶ is —N(R^(B))₂, wherein each instance of R^(B) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, and optionally substituted aryl, or a nitrogen protecting group, or two R^(B) taken together with the intervening nitrogen form a heterocycle. In certain embodiments, G⁶ is NH₂. In certain embodiments, G⁶ is NHR^(B), wherein R^(B) is optionally substituted C₁-C₆ alkyl. In certain embodiments, G⁶ is NHCH₃ or NHC₂H₅. In certain embodiments, G⁶ is NHR^(B), wherein R^(B) is a nitrogen protecting group.

As generally defined herein, G⁷ is independently selected from hydrogen, halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A). In certain embodiments, G⁷ is H. In certain embodiments, G⁷ is halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A). In certain embodiments, G⁷ is halogen. In certain embodiments, G⁷ is optionally substituted C₁-C₆ alkyl. In certain embodiments, G⁷ is methyl, ethyl, or n-propyl. In certain embodiments, G⁷ is —OR^(A), wherein R^(A) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, or an oxygen protecting group when attached to an oxygen, or a sulfur protecting group when attaching to sulfur. In certain embodiments, G⁷ is —OH. In certain embodiments, G⁷ is —OR^(A), wherein R^(A) is optionally substituted C₁-C₆ alkyl. In certain embodiments, G⁷ is —OCH₃ or —OC₂H₅. In certain embodiments, G⁷ is —OR^(A), wherein R^(A) is an oxygen protecting group. In certain embodiments, G⁷ is —N(R^(B))₂, wherein each instance of R^(B) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, and optionally substituted aryl, or a nitrogen protecting group, or two R^(B) taken together with the intervening nitrogen form a heterocycle. In certain embodiments, G⁷ is NH₂. In certain embodiments, G⁷ is NHR^(B), wherein R^(B) is optionally substituted C₁-C₆ alkyl. In certain embodiments, G⁷ is NHCH₃ or NHC₂H₅. In certain embodiments, G⁷ is NHR^(B), wherein R^(B) is a nitrogen protecting group.

In certain embodiments, G⁶ and G⁷ are taken together with their intervening atoms to form an optionally substituted carbocycle or heterocycle. In certain embodiments, G⁶ and G⁷ are taken together with their intervening atoms to form an optionally substituted carbocycle. In certain embodiments, G⁶ and G⁷ are taken together with their intervening atoms to form an optionally substituted 5-membered carbocycle. In certain embodiments, G⁶ and G⁷ are taken together with their intervening atoms to form an optionally substituted 6-membered carbocycle. In certain embodiments, G⁶ and G⁷ are taken together with their intervening atoms to form an optionally substituted heterocycle. In certain embodiments, G⁶ and G⁷ are taken together with their intervening atoms to form an optionally substituted 5-membered heterocycle with one heteroatom of S, N, or O. In certain embodiments, G⁶ and G⁷ are taken together with their intervening atoms to form an optionally substituted 5-membered heterocycle with two heteroatom each independently selected from the group of S, N, and O. In certain embodiments, G⁶ and G⁷ are taken together with their intervening atoms to form an optionally substituted 6-membered carbocycle with one heteroatom of S, N, or O. In certain embodiments, G⁶ and G⁷ are taken together with their intervening atoms to form an optionally substituted 6-membered carbocycle with two heteroatoms each independently selected from the group consisting of S, N, and O.

In certain embodiments, the compounds described herein are of formula (II)

or a salt thereof,

wherein

each of G⁹ and G¹⁰ is independently selected from hydrogen, halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A).

As generally defined herein, G⁹ is independently selected from hydrogen, halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A). In certain embodiments, G⁹ is H. In certain embodiments, G⁹ is halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A). In certain embodiments, G⁹ is halogen. In certain embodiments, G⁹ is optionally substituted C₁-C₆ alkyl. In certain embodiments, G⁹ is methyl, ethyl, or n-propyl. In certain embodiments, G⁹ is —OR^(A), wherein R^(A) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, or an oxygen protecting group when attached to an oxygen, or a sulfur protecting group when attaching to sulfur. In certain embodiments, G⁹ is —OH. In certain embodiments, G⁹ is —OR^(A), wherein R^(A) is optionally substituted C₁-C₆ alkyl. In certain embodiments, G⁹ is —OCH₃ or —OC₂H₅. In certain embodiments, G⁹ is —OR^(A), wherein R^(A) is an oxygen protecting group. In certain embodiments, G⁹ is —N(R^(B))₂, wherein each instance of R^(B) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, and optionally substituted aryl, or a nitrogen protecting group, or two R^(B) taken together with the intervening nitrogen form a heterocycle. In certain embodiments, G⁹ is NH₂. In certain embodiments, G⁹ is NHR^(B), wherein R^(B) is optionally substituted C₁-C₆ alkyl. In certain embodiments, G⁹ is NHCH₃ or NHC₂H₅. In certain embodiments, G⁹ is NHR^(B), wherein R^(B) is a nitrogen protecting group.

As generally defined herein, G¹⁰ is independently selected from hydrogen, halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A). In certain embodiments, G¹⁰ is H. In certain embodiments, G¹⁰ is halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A). In certain embodiments, G¹⁰ is halogen. In certain embodiments, G¹⁰ is optionally substituted C₁-C₆ alkyl. In certain embodiments, G¹⁰ is methyl, ethyl, or n-propyl. In certain embodiments, G¹⁰ is —OR^(A), wherein R^(A) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, or an oxygen protecting group when attached to an oxygen, or a sulfur protecting group when attaching to sulfur. In certain embodiments, G¹⁰ is —OH. In certain embodiments, G¹⁰ is —OR^(A), wherein R^(A) is optionally substituted C₁-C₆ alkyl. In certain embodiments, G¹⁰ is —OCH₃ or —OC₂H₅. In certain embodiments, G¹⁰ is —OR^(A), wherein R^(A) is an oxygen protecting group. In certain embodiments, G¹⁰ is —N(R^(B))₂, wherein each instance of R^(B) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, and optionally substituted aryl, or a nitrogen protecting group, or two R^(B) taken together with the intervening nitrogen form a heterocycle. In certain embodiments, G¹⁰ is NH₂. In certain embodiments, G¹⁰ is NHR^(B), wherein R^(B) is optionally substituted C₁-C₆ alkyl. In certain embodiments, G¹⁰ is NHCH₃ or NHC₂H₅. In certain embodiments, G¹⁰ is NHR^(B), wherein R^(B) is a nitrogen protecting group. In certain embodiments, G¹⁰ is —C(O)R^(C), wherein R^(C) is hydrogen or optionally substituted C₁₋₆ alkyl. In certain embodiments, G¹⁰ is —C(O)H. In certain embodiments, G¹⁰ is —C(O)R^(C), wherein R^(C) is optionally C₁₋₆ substituted alkyl. In certain embodiments, G¹⁰ is optionally substituted alkenyl. In certain embodiments, G¹⁰ is of the formula

wherein R^(A) is as defined herein; and each instance of R^(10a) and R^(10b) is independently hydrogen, halogen, or optionally substituted C₁₋₆ alkyl.

As generally defined herein, each instance of R^(10a) and R^(10b) is independently hydrogen, halogen, or optionally substituted C₁₋₆ alkyl. In certain embodiments, R^(10a) is hydrogen. In certain embodiments, R^(10a) is halogen. In certain embodiments, R^(10b) is hydrogen. In certain embodiments, R^(10b) is halogen. In certain embodiments, G¹⁰ is one of the following formulae:

As generally defined herein, each instance of R^(A) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, or an oxygen protecting group when attached to an oxygen, or a sulfur protecting group when attaching to sulfur. In certain embodiments, R^(A) is hydrogen. In certain embodiments, R^(A) is optionally substituted C₁-C₆ alkyl. In certain embodiments, R^(A) is methyl or ethyl. In certain embodiments, R^(A) is an oxygen protecting group. In certain embodiments, R^(A) is a sulfur protecting group.

As generally defined herein, each instance of R^(B) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, or a nitrogen protecting group, or two R^(B) taken together with the intervening nitrogen form a heterocycle. In certain embodiments, R^(B) is hydrogen. In certain embodiments, R^(B) is optionally substituted C₁-C₆ alkyl. In certain embodiments, R^(B) is methyl or ethyl. In certain embodiments, R^(B) is a nitrogen protecting group. In certain embodiments, two R^(B) are taken together with the intervening nitrogen form a heterocycle.

As generally defined herein, each instance of R^(C) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, or optionally substituted heteroaryl. In certain embodiments, R^(C) is hydrogen. In certain embodiments, R^(C) is optionally substituted C₁-C₆ alkyl. In certain embodiments, R^(C) is methyl or ethyl. In certain embodiments, R^(C) is a nitrogen protecting group. In certain embodiments, two R^(C) are taken together with the intervening nitrogen form a heterocycle.

In certain embodiments of formulae (I) and (II), X¹—X² is —CH═CH—. In certain embodiments of formula (I), X³—X⁴ is —CH═CH—.

In certain embodiments of formula (II), G⁹ is hydrogen and G¹⁰ is optionally substituted alkenyl. In certain embodiments, G¹⁰ is of Formula (G-i).

In certain embodiments, the provided compounds are of one of following formulae:

In certain embodiments of formulae (II-a) to (II-f), G⁵ is hydrogen. In certain embodiments of formulae (II-a) to (II-f), G⁸ is hydrogen. In certain embodiments of formulae (II-a) to (II-f), G⁹ is hydrogen. In certain embodiments of formulae (II-a) to (II-f), G⁵, G⁸, and G⁹ are all hydrogen. In certain embodiments of formula (II-e), R^(A) is hydrogen or optionally substituted C₁₋₆ alkyl. In certain embodiments of formula (II-e), R^(A) is hydrogen. In certain embodiments of formula (II-e), R^(A) is methyl or ethyl.

In certain embodiments of formula (II-a) and (II-b), G¹⁰ is of the formula:

wherein R^(A) is as defined herein; and each instance of R^(10a) and R^(10b) is independently hydrogen, halogen, or optionally substituted C₁₋₆ alkyl. In certain embodiments of formula (II-a) and (II-b), G¹⁰ is of one of following the formulae:

Exemplary compounds of formulae (I) and (II) are shown in Table 1:

TABLE 1 Exemplary compounds of formulae (I) and (II).

(1)

(T2)

(T3)

(T4)

(T5)

(T6)

(T7)

(T8)

(T9)

(T10)

(T11)

(T12)

(T13)

(T14)

(T15)

(T16)

(T17)

(T18)

(T19)

(T20)

(T21)

(T22)

(T23)

(T24)

(T25)

(T26)

(T27)

(T28)

(T29)

(T30)

(T31)

(T32)

(T33)

(T34)

(T35)

(T36)

(T37)

(T38)

(T39)

(T40)

(T41)

(T42)

(T43)

(T44)

(T45)

(T46)

(T47)

(T48)

(T49)

(T50)

(T51)

(T52)

(T53)

(T54)

(T55)

(T56)

(T57)

(T58)

(T59)

(T60)

(T61)

(T62)

(T63)

(T64)

(T65)

(T66)

(T67)

(T68)

(T69)

(T70)

(T71)

(T72)

(T73)

(T74)

(T75)

(T76)

(T77)

(T78)

(T79)

(T80)

(T81)

(T82)

(T83)

(T84)

(T85)

(T86)

(T87)

(T88)

(T89)

(T90)

(T91)

(T92)

(T93)

(2)

(T95)

(T96)

(T97)

(T98)

(T99)

(T100)

(T101)

(T102)

(T103)

(T104)

(T105)

(T106)

(T107)

(T108)

(T109)

(T110)

(T111)

(T112)

(T113)

(T114)

(T115)

(T116)

(T117)

(T118)

(T119)

(T120)

(T121)

(T122)

(T123)

(T124)

(T125)

(T126)

(T127)

(T128)

(T129)

(T130)

(T131)

(T132)

(T133)

(T134)

(T135)

(T136)

(T137)

(T138)

(T139)

(T140)

(T141)

(T142)

(T143)

(T144)

(T145)

(T146)

(T147)

(T148)

(T149)

(T150)

(T151)

(T152)

(T153)

(T154)

(T155)

(T156)

(T157)

(T158)

(T159)

(T160)

(T161)

(T162)

(T163)

Coumarin-fused cyclooctyne probes were used to detect azide compounds, including the azido-annexed biomolecules. After SPAAC reaction with an azide compound under copper-free condition, the formation of triazole ring will release the fluorescence quenching, and lead to a fluorogenic phenomenon. Compound 1 is an example of such type of probes that undergo SPAAC with azides to give fluorescent triazole products.

In another embodiment, a green-emitting coumarin-based fluorogenic compound 2 was used. An indolium moiety as an electron-withdrawing group is introduced to the 3-position of the coumarin core. Upon excitation, bathochromic shift of the emission wavelength by an ICT process is anticipated.

In another aspect, the present disclosure provides compounds of formula

-   -   or a salt thereof,     -   wherein     -   X₁, X₂, X₃, and X₄ are in a 8-membered carbocycle or         heterocycle; provided that when the 8-membered ring is a         heterocycle, three of X₁, X₂, X₃, and X₄ are carbon atoms, and         one of X₁, X₂, X₃, and X₄ is N, O, P, or S;     -   each of G¹, G², G³ and G⁴ is independently selected from         hydrogen, halogen, optionally substituted C₁-C₆ alkyl,         optionally substituted alkenyl, optionally substituted alkynyl,         optionally substituted heterocyclyl, optionally substituted         aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A),         —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C),         —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C),         —SO₂R^(A), —SO₂N(R^(B))₂, ═O, ═NOH, ═N—OR^(A), ═N—NH₂,         ═N—NHR^(B), ═N—N(R^(B))₂, and —NHSO₂R^(A); or G¹ and G² are         taken together with their intervening atoms to form an         optionally substituted carbocycle or heterocycle; or G³ and G⁴         are taken together with their intervening atoms to form an         optionally substituted carbocycle or heterocycle;     -   each of G⁵ and G⁸ is independently selected from hydrogen,         halogen, optionally substituted C₁-C₆ alkyl, optionally         substituted alkenyl, optionally substituted alkynyl, optionally         substituted heterocyclyl, optionally substituted aryl,         optionally substituted heteoaryl, —OR^(A), —CH₂OR^(A),         —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C),         —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C),         —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A);     -   each of G⁶ and G⁷ is independently selected from hydrogen,         halogen, optionally substituted C₁-C₆ alkyl, optionally         substituted alkenyl, optionally substituted alkynyl, optionally         substituted heterocyclyl, optionally substituted aryl,         optionally substituted heteoaryl, —OR^(A), —CH₂OR^(A),         —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C),         —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C),         —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A), or G⁶ and G⁷ are         taken together with their intervening atoms to form an         optionally substituted carbocycle or heterocycle;     -   each of G⁹ and G¹⁰ is independently selected from hydrogen,         halogen, optionally substituted C₁-C₆ alkyl, optionally         substituted alkenyl, optionally substituted alkynyl, optionally         substituted heterocyclyl, optionally substituted aryl,         optionally substituted heteroaryl, optionally substituted         heteoaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A),         —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂,         —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂,         and —NHSO₂R^(A).     -   each of R¹¹ and R¹² is independently selected from the group         consisting of hydrogen, halogen, optionally substituted C₁-C₆         alkyl, optionally substituted alkenyl, optionally substituted         alkynyl, optionally substituted heterocyclyl, optionally         substituted aryl, optionally substituted heteoaryl, optionally         substituted heterocyclylalkyl, optionally substituted arylalkyl,         optionally substituted heteoarylalkyl, —OR^(A), —CH₂OR^(A),         —(CH₂)_(t)OC(O)R^(C), —SR^(A), —N(R^(B))₂,         —(CH₂)_(t)—N(R^(B))C(O)R^(C), —(CH₂)_(t)—C(O)N(R^(B))₂, —CN,         —NO₂, —C(O)R^(C), —(CH₂)_(t)C(O)OR^(A), —S(O)R^(C), —SO₂R^(A),         —SO₂N(R^(B))₂, and —NHSO₂R^(A);     -   t is an integer of 1 to 5, inclusive;     -   each instance of R^(A) is independently hydrogen, optionally         substituted C₁-C₆ alkyl, optionally substituted alkenyl,         optionally substituted alkynyl, optionally substituted         heterocyclyl, optionally substituted aryl, or an oxygen         protecting group when attached to an oxygen, or a sulfur         protecting group when attaching to sulfur;     -   each instance of R^(B) is independently hydrogen, optionally         substituted C₁-C₆ alkyl, optionally substituted alkenyl,         optionally substituted alkynyl, optionally substituted         heterocyclyl, optionally substituted aryl, or a nitrogen         protecting group, or two R^(B) taken together with the         intervening nitrogen form a heterocycle; and     -   each instance of R^(C) is independently hydrogen, optionally         substituted C₁-C₆ alkyl, optionally substituted alkenyl,         optionally substituted alkynyl, optionally substituted         heterocyclyl, optionally substituted aryl, or optionally         substituted heteroaryl; and     -   provided that when G¹ and G² are taken together with their         intervening atoms to form an optionally substituted phenyl, G⁶         and G⁷ are taken together with their intervening atoms to form         an optionally substituted heterocycle and X⁴ is not N.

For compounds of formula (II), when G¹ and G² are taken together with their intervening atoms to form an optionally substituted phenyl, G⁶ and G⁷ are taken together with their intervening atoms to form an optionally substituted heterocycle and X⁴ is not N.

For compounds of formula (II), variables X₁, X₂, X₃, X₄, G¹, G², G³, G⁵, G⁶, G⁷, G⁸, G⁹, and G¹⁰ are as defined herein.

As generally defined herein, R¹¹ is independently selected from hydrogen, halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteoaryl, optionally substituted heterocyclylalkyl, optionally substituted arylalkyl, optionally substituted heteoarylalkyl, —OR^(A), —CH₂OR^(A), —(CH₂)_(t)OC(O)R^(C), —SR^(A), —N(R^(B))₂, —(CH₂)_(t)—N(R^(B))C(O)R^(C), —(CH₂)_(t)—C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —(CH₂)_(t)C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A). In certain embodiments, R¹¹ is H. In certain embodiments, R¹¹ is halogen. In certain embodiments, R¹¹ is optionally substituted C₁-C₆ alkyl. In certain embodiments, R¹¹ is methyl, ethyl, or n-propyl. In certain embodiments, R¹¹ is optionally substituted heterocyclylalkyl, optionally substituted arylalkyl, optionally substituted heteoarylalkyl. In certain embodiments, R¹¹ is optionally substituted arylalkyl. In certain embodiments, R¹¹ is —CH₂Ph. In certain embodiments, R¹¹ is —(CH₂)_(t)—C(O)N(R^(B))₂. In certain embodiments, R¹¹ is —CH₂—C(O)NHR^(B), wherein R^(B) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted heterocyclyl, optionally substituted aryl, or optionally substituted heteoaryl. In certain embodiments, R¹¹ is —CH₂—C(O)NHR^(B), wherein R^(B) is of formula

In certain embodiments, R¹¹ is —OR^(A), wherein R^(A) is independently hydrogen or optionally substituted C₁-C₆ alkyl. In certain embodiments, R¹¹ is —OH. In certain embodiments, R¹¹ is —OR^(A), wherein R^(A) is optionally substituted C₁-C₆ alkyl. In certain embodiments, R¹¹ is —OCH₃ or —OC₂H₅. In certain embodiments, R¹¹ is —OR^(A), wherein R^(A) is an oxygen protecting group. In certain embodiments, R¹¹ is —N(R^(B))₂, wherein each instance of R^(B) is independently hydrogen or optionally substituted C₁-C₆ alkyl. In certain embodiments, R¹¹ is NH₂. In certain embodiments, R¹¹ is NHR^(B), wherein R^(B) is optionally substituted C₁-C₆ alkyl. In certain embodiments, R¹¹ is NHCH₃ or NHC₂H₅. In certain embodiments, R¹¹ is NHR^(B), wherein R^(B) is a nitrogen protecting group.

As generally defined herein, R¹² is independently selected from hydrogen, halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteoaryl, optionally substituted heterocyclylalkyl, optionally substituted arylalkyl, optionally substituted heteoarylalkyl, —OR^(A), —CH₂OR^(A), —(CH₂)_(t)OC(O)R^(C), —SR^(A), —N(R^(B))₂, —(CH₂)_(t)—N(R^(B))C(O)R^(C), —(CH₂)_(t)—C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —(CH₂)_(t)C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A). In certain embodiments, R¹² is H. In certain embodiments, R¹² is halogen. In certain embodiments, R¹² is optionally substituted C₁-C₆ alkyl. In certain embodiments, R¹² is methyl, ethyl, or n-propyl. In certain embodiments, R¹² is optionally substituted heterocyclylalkyl, optionally substituted arylalkyl, optionally substituted heteoarylalkyl. In certain embodiments, R¹² is optionally substituted arylalkyl. In certain embodiments, R¹² is —CH₂Ph. In certain embodiments, R¹² is —(CH₂)_(t)—C(O)N(R^(B))₂. In certain embodiments, R¹² is —CH₂—C(O)NHR^(B), wherein R^(B) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted heterocyclyl, optionally substituted aryl, or optionally substituted heteoaryl. In certain embodiments, R¹² is —CH₂—C(O)NHR^(B), wherein R^(B) is of formula

In certain embodiments, R¹² is —OR^(A), wherein R^(A) is independently hydrogen or optionally substituted C₁-C₆ alkyl. In certain embodiments, R¹² is —OH. In certain embodiments, R¹² is —OR^(A), wherein R^(A) is optionally substituted C₁-C₆ alkyl. In certain embodiments, R¹² is —OCH₃ or —OC₂H₅. In certain embodiments, R¹² is —OR^(A), wherein R^(A) is an oxygen protecting group. In certain embodiments, R¹² is —N(R^(B))₂, wherein each instance of R^(B) is independently hydrogen or optionally substituted C₁-C₆ alkyl. In certain embodiments, R¹² is NH₂. In certain embodiments, R¹² is NHR^(B), wherein R^(B) is optionally substituted C₁-C₆ alkyl. In certain embodiments, R¹² is NHCH₃ or NHC₂H₅. In certain embodiments, R¹² is NHR^(B), wherein R^(B) is a nitrogen protecting group.

In certain embodiments of formula (I) or (II),

is —CH₂—CH₂—CH₂—CH₂—.

The present disclosure also relates to synthetic methods for preparation of benzocyclooctyne compounds as described herein. The present disclosure also demonstrates that such benzocyclooctyne compounds react with organic azides to form triazole products with enhanced fluorescence.

FIG. 2 shows the synthesis of Compound 1 comprising steps: (a) treatment of 1-benzosuberone with potassium nitrate in concentrated sulfuric acid at 0° C. to afford compound 4; (Murineddu, G., et al. J. Med. Chem. 2005, 48, 7351.)

(b) treatment of compound 4 with tin metal as the reducing reagent in concentrated HCl to afford an amine intermediate, followed by diazotized with sodium nitrite in acid condition, and hydroxylation to give compound 5; (Smith, P. A. S.; Berry, W. L. J. Org. Chem. 1961, 26, 27.)

(c) treatment of compound 5 in anhydrous N,N-dimethylformamide (DMF) with benz bromide in the presence of potassium carbonate to afford a benzyloxy compound 6:

(d) ring expansion reaction of compound 6 using (trimethylsilyl)diazomethane in the presence of BF₃.OEt₂ at 0° C. to afford a cyclooctanone product 7:

(e) treatment of compound 7 with NaBH₄ in methanol, followed by treatment with triisopropylsilyl trifluoromethylsulfonate (TIPSOTf) in the presence of 2,6-lutidine, to give a silyl ether 8:

(f) removal of the benzyl group in compound 8 by hydrogenation, followed by treatment with anhydrous MgCl₂, triethylamine and paraformaldehyde in acetonitrile to afford a salicylaldehyde product 9:

(g) treatment of compound 9 with diethyl malonate, piperidine and acetic acid in ethanol to afford a coumarin product 10:

(h) treating compound 10 in the media of acetic acid and concentrated HCl to give compound 11:

(i) Swern oxidation of compound 11 to give ketone 12:

(j) converting compound 12 to an enol triflate, followed by treatment with potassium hexamethyldisilazide (KHMDS) to afford Compound 1.

In one embodiment, Compound 1 reacted with benzyl azide in ethanol/water (1:1) in the absence of copper(I) catalyst to afford the cycloaddition product as a mixture of two triazole reigoisomers 3a and 3b. These two trizaole isomers were separated, and their photophysical properties were investigated, respectively. Similar to Compound 1, compounds 3a and 3b exhibited an absorption band at λ_(max)=330 nm, albeit with substantially higher extinction coefficients (˜2.5 fold). Upon irradiation, compounds 1, 3a and 3b all showed fluorescence emission at λX_(max)=400 nm. The quantum yields of triazole compounds 3a (Φ_(f)=0.23) and 3b (Φ_(f)=0.22) were 20-fold higher than Compound 1 (Φ_(f)=0.011). The alkyne-annexed coumarin compound A exhibits the optical property similar to Compound 1; however, compound A requires copper(I) catalyst to proceed the CuAAC reaction.

The cycloaddition of compound 1 with benzyl azide was a second-order reaction. FIG. 3 a shows the time course of normalized fluorescence intensity during the reaction. FIG. 3 b shows the progress of the cycloaddition reaction in CD₃CN (19 mM) as monitored by the integration area of the benzylic proton signals in the ¹H-NMR spectra. The second-order rate constant (k) was determined to be 0.015 M⁻¹s⁻¹ at 25° C. In comparison, Compound 1 is more reactive than 3-alkoxycyclooctayne (OCT, k=0.002 M⁻¹s⁻¹) but inferior to 11-alkoxy-dibenzocyclooctyne (DIBO, k=0.06 M⁻¹s⁻¹). (Agard, et al., J. Am. Chem. Soc. 2004, 126, 15046; Ning, et al., Angew. Chem. Int. Ed. 2008, 47, 2253).

For biological applications, a fluorogenic compound 2 exhibits the absorption and fluorescence in long wavelengths (˜500 nm). The triazole product derived from SPAAC reaction of 2 shows high fluorescence quantum yield in aqueous solution. Compound C containing an indolium moiety at the 3-position of the 7-alkynylcoumarin scaffold was used as a model of compound 2.

FIG. 4 shows the synthesis of Compound C comprising steps:

(a) treatment of 2,4-dihydroxybenzaldehyde with diethyl glutaconate in the presence of piperidine to afford a coumarin ester 13:

(b) treatment of Compound 13 with trifluoromethylsulfonic anhydride (Tf₂O) and pyridine to afford a triflate 14:

(c) Sonogashira reaction of Compound 14 with trimethylsilylacetylene in the presence of PdCl₂(PPh₃)₂, CuI and diisopropylethylamine to afford a alkynyl-annexed coumarin 15:

(d) ozonolysis of Compound 15 to give Compound 16:

(e) base-mediated condensation reaction of Compound 16 with N-(4-sulfonatobutyl)-2,3,3-trimethylindolium 17, followed by desilylstion with tetrabutylammonium fluoride, to give compound C.

Compound C showed an absorption at λ_(max) 500 nm (ε=8,600 M⁻¹ cm⁻¹) and a weak fluorescence at λ_(max) 515 nm (Φ_(f)=0.017). Under standard CuAAC conditions, compound C reacted with benzyl azide to give triazole product 18, which showed an absorption at λ_(max) 500 nm (Σ=32,000 M⁻¹ cm⁻¹) and a strong fluorescence at λ_(max) 520 nm (Φ_(f)=0.56) in aqueous solution.

In one aspect, the present disclosure relates to methods (in vivo or in vitro) for detecting and/or imaging organic molecules or biomolecules, particularly those that contains azide groups. Examples include, but are not limited to, amino acids, polypeptides (including peptides and proteins), sugars (including monosaccharides, oligosaccharides, and polysaccharides), and the like. Such molecules may contain or may be modified to contain at least one azide group.

In certain embodiments, the present disclosure provides a method for imaging an azide-containing molecule as described herein. The method can comprise: (a) incubating a compound as described herein (e.g., Compound 1 or Compound 2) with a sample containing an azide-containing molecule under conditions allowing for ligation of the compound to an azido group of the molecule to form a triazole product; and (b) detecting a fluorescent signal released from the triazole product.

In certain embodiments, the present disclosure provides methods (in vivo or in vitro) for detecting an azide-containing molecule as described herein in a sample, such as a biosample. The method comprises:(a) contacting a compound as described herein (e.g., Compound 1 or Compound 2) to a sample suspected of having an azide-containing molecule; (b) detecting a level of a fluorescent signal released from the sample, and

(c) determining presence of the azide-containing molecule in the sample. An enhanced fluorescent signal as compared to a level of the fluorescent signal in the absence of the compound indicates presence of the azide-containing molecule.

In certain embodiments of the imaging and/or detecting methods described herein, the incubating step is carried out in the absence of a metal catalyst. In certain embodiments, the compound is covalently linked to the azido group. In certain embodiments, the sample contains cells and the azide-containing molecule is located on or inside the cells. In certain embodiments, the azide-containing molecule is a biomolecule molecule. In certain embodiments, the biomolecule is a DNA, RNA, protein or glycan. In certain embodiments, the biomolecule is on a cell surface. In certain embodiments, the biomolecule is intracellular. In certain embodiments, the biomolecule is of avian, mammalian, viral, parasitical, fungal, or bacterial origin. In certain embodiments, the biomolecule is of human origin. In certain embodiments, the biomolecule is associated with a disease or physical condition. In certain embodiments, the disease or physical condition is selected from the group consisting of cancer (such as malignant tumor), rheumatoid arthritis, and inflammation. In certain embodiments, the molecule is an organic molecule.

In some embodiments, the present present disclosure is used for in vivo imaging, e.g., to determine the metabolic or other state of a cell in an organism (e.g., a human). As one non-limiting example, a subject method may be applied to in vivo imaging of cancer cells in an individual (e.g., a mammal, including rodents, lagomorphs, felines, canines, equines, bovines, ovines, caprines, non-human primates, and humans).

Exemplary cancers include, but are not limited to, lung cancer, prostate cancer, breast cancer, colorectal cancer, ovarian cancer, lymphoma, and leukemia.

The term “inflammation” refers to those diseases, disorders or conditions that are characterized by signs of pain (dolor, from the generation of noxious substances and the stimulation of nerves), heat (calor, from vasodilatation), redness (rubor, from vasodilatation and increased blood flow), swelling (tumor, from excessive inflow or restricted outflow of fluid), and/or loss of function (functio laesa, which can be partial or complete, temporary or permanent. Inflammation takes on many forms and includes, but is not limited to, acute, adhesive, atrophic, catarrhal, chronic, cirrhotic, diffuse, disseminated, exudative, fibrinous, fibrosing, focal, granulomatous, hyperplastic, hypertrophic, interstitial, metastatic, necrotic, obliterative, parenchymatous, plastic, productive, proliferous, pseudomembranous, purulent, sclerosing, seroplastic, serous, simple, specific, subacute, suppurative, toxic, traumatic, and/or ulcerative inflammation.

Exemplary inflammations include, but are not limited to, inflammation associated with acne, anemia (e.g., aplastic anemia, haemolytic autoimmune anaemia), asthma, arteritis (e.g., polyarteritis, temporal arteritis, periarteritis nodosa, Takayasu's arteritis), arthritis (e.g., crystalline arthritis, osteoarthritis, psoriatic arthritis, gouty arthritis, reactive arthritis, rheumatoid arthritis and Reiter's arthritis), ankylosing spondylitis, amylosis, amyotrophic lateral sclerosis, autoimmune diseases, allergies or allergic reactions, atherosclerosis, bronchitis, bursitis, chronic prostatitis, conjunctivitis, Chagas disease, chronic obstructive pulmonary disease, cermatomyositis, diverticulitis, diabetes (e.g., type I diabetes mellitus, type 2 diabetes mellitus), a skin condition (e.g., psoriasis, eczema, burns, dermatitis, pruritus (itch)), endometriosis, Guillain-Barre syndrome, infection, ischaemic heart disease, Kawasaki disease, glomerulonephritis, gingivitis, hypersensitivity, headaches (e.g., migraine headaches, tension headaches), ileus (e.g., postoperative ileus and ileus during sepsis), idiopathic thrombocytopenic purpura, interstitial cystitis (painful bladder syndrome), gastrointestinal disorder (e.g., selected from peptic ulcers, regional enteritis, diverticulitis, gastrointestinal bleeding, eosinophilic gastrointestinal disorders (e.g., eosinophilic esophagitis, eosinophilic gastritis, eosinophilic gastroenteritis, eosinophilic colitis), gastritis, diarrhea, gastroesophageal reflux disease (GORD, or its synonym GERD), inflammatory bowel disease (IBD) (e.g., Crohn's disease, ulcerative colitis, collagenous colitis, lymphocytic colitis, ischaemic colitis, diversion colitis, Behcet's syndrome, indeterminate colitis) and inflammatory bowel syndrome (IBS)), lupus, multiple sclerosis, morphea, myeasthenia gravis, myocardial ischemia, nephrotic syndrome, pemphigus vulgaris, pernicious aneaemia, peptic ulcers, polymyositis, primary biliary cirrhosis, neuroinflammation associated with brain disorders (e.g., Parkinson's disease, Huntington's disease, and Alzheimer's disease), prostatitis, chronic inflammation associated with cranial radiation injury, pelvic inflammatory disease, reperfusion injury, regional enteritis, rheumatic fever, systemic lupus erythematosus, schleroderma, scierodoma, sarcoidosis, spondyloarthopathies, Sjogren's syndrome, thyroiditis, transplantation rejection, tendonitis, trauma or injury (e.g., frostbite, chemical irritants, toxins, scarring, burns, physical injury), vasculitis, vitiligo and Wegener's granulomatosis. In certain embodiments, the inflammatory disorder is selected from arthritis (e.g., rheumatoid arthritis), inflammatory bowel disease, inflammatory bowel syndrome, asthma, psoriasis, endometriosis, interstitial cystitis and prostatistis. In certain embodiments, the inflammatory condition is an acute inflammatory condition (e.g., for example, inflammation resulting from infection). In certain embodiments, the inflammatory condition is a chronic inflammatory condition (e.g., conditions resulting from asthma, arthritis and inflammatory bowel disease).

The azide-containing molecules to be examined in the methods described herein can be naturally occurring. Alternatively, it can be prepared by modifying a molecule that originally does not contain azide groups using methods known in the art. The azide-containing molecules can be on a cell surface or inside a cell, which can be either a cultured cell or a cell within including a host animal, e.g., a mammalian animal, such as a murine host (e.g., rat, mouse), hamster, canine, feline, bovine, swine, and the like). In some embodiments, the azide-containing molecule is present in vitro in a cell-free reaction. In other embodiments, the molecule is present in a cell and/or displayed on the surface of a cell. In many embodiments of interest, the azide-containing molecule is in a living cell; on the surface of a living cell; in a living organism, e.g., in a living multicellular organism. Suitable living cells include cells that are part of a living multicellular organism; cells isolated from a multicellular organism; immortalized cell lines; and the like.

Where the azide-containing molecule is a polypeptide, the polypeptide may be composed of D-amino acids, L-amino acids, or both, and may be further modified, either naturally, synthetically, or recombinantly, to include other moieties. For example, the polypeptide may be a lipoprotein, a glycoprotein, or other such modified protein.

In general, the azide-containing molecule comprises at least one azide for reaction with modified cycloalkyne according to the present disclosure, but may comprise 2 or more, 3 or more, 5 or more, 10 or more azides. The number of azides that may be present in a target molecule will vary according to the intended application of the final product of the reaction, the nature of the azide-containing molecule itself, and other considerations which will be readily apparent to the ordinarily skilled artisan in practicing the present disclosure as disclosed herein.

In certain embodiments, the compounds provided herein can be further conjugated with a therapeutic agent (e.g., an anti-cancer drug) to deliver the therapeutic agent to a target substrate containing an azide moiety. In certain embodiments, the compounds as described herein are used in delivering cancer drugs.

In certain embodiments, the exemplary compound in any of the methods as described herein (such as imaging or detecting biomolecule) is of the formula

EXAMPLES Example 1 Synthesis of Exemplary Compounds Methods and Material

All the reagents were commercially available and used without further purification unless indicated otherwise. All solvents were anhydrous grade unless indicated otherwise. All non-aqueous reactions were carried out in oven-dried glassware under a slight positive pressure of argon unless otherwise noted. Reactions were magnetically stirred and monitored by thin-layer chromatography on silica gel. Column chromatography was performed on silica gel of 40-63 μm particle size. Yields are reported for spectroscopically pure compounds. Melting points were recorded on an Electrothermal MEL-TEMP® 1101D melting point apparatus and are not corrected. NMR spectra were recorded on Bruker AVANCE 600 spectrometer. Chemical shifts are given in δ values relative to tetramethylsilane (TMS); coupling constants J are given in Hz. Internal standards were CDCl₃ (δ_(H)=7.24), MeOH-d₄ (δ_(H)=3.31) or D₂O (δ_(H)=4.79) for ¹H-NMR spectra, CDCl₃ (δ, =77.0 of central line) or MeOH-d₄ (δ_(c)=49.15) for ¹³C-NMR spectra. The splitting patterns are reported as s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet), br (broad) and dd (double of doublets). IR spectra were recorded on a Thermo Nicolet 380 FT-IR spectrometer. Optical rotations were recorded on a Perkin-Elmer Model 341 polarimeter. High resolution ESI mass spectra were recorded on a Bruker Daltonics spectrometer.

3-Nitro-6,7,8,9-tetrahydrobenzo[7]annulen-5-one (4)

A solution of KNO₃ (2.8 g, 27.7 mmol) in concentrated H₂SO₄ (7.5 mL) was added dropwise to a mixture of benzosuberone (4.0 g, 25 mmol) in concentrated H₂SO₄ (28 mL) at 0° C. in 30 min. The mixture was stirred for 1 h at 0° C., and then the poured into crushed ice. The precipitate was filtered, rinsed with water and dried. The crude product was purified by column chromatography on silica gel (EtOAc/hexane, 1:4) to afford the pure nitro product 4 (3.69 g, 72%). C₁₁H₁₁NO₃; white needles, mp 90-92° C. (lit.^(S1) mp 89-90° C.) (Murineddu, G., et al. J. Med. Chem. 2005, 48, 7351.); TLC (EtOAc/hexane, 1:4) R_(f)=0.31; ¹H NMR (600 MHz, CDCl₃) δ 8.53 (1H, d, J=2.5 Hz), 8.22 (1H, dd, J=8.3, 2.5 Hz), 7.37 (1H, d, J=8.3 Hz), 3.01 (2H, t, J=6.4 Hz), 2.77 (2H, t, J=6.1 Hz), 1.94-1.90 (2H, m), 1.85-1.81 (2H, m); ¹³C NMR (150 MHz, CDCl₃) δ 203.4, 148.0, 147.0, 139.8, 131.0, 126.2, 123.9, 40.4, 32.4, 24.7, 20.5.

3-Hydroxy-6,7,8,9-tetrahydrobenzo[7]annulen-5-one (5)

A mixture of compound 4 (2.05 g, 10 mmol) and Sn (8.31 g, 70 mmol) in concentrated HCl (45 mL) and ethanol (25 mL) was heated at reflux for 50 min. The mixture was cooled to room temperature, and the solution was basified with 30% NaOH aqueous solution. The mixture was filtered through a pad of Celite, and washed with ethanol. The filtrate was extracted with EtOAc (5×50 mL). The combined organic extracts were washed with brine (100 mL), dried over MgSO4, filtered, and concentrated under reduced pressure to afford a practically pure amine product (1.45 g) as yellowish solids.

To a cold (0° C.) solution of the above-prepared amine compound (1.45 g, 8.3 mmol) in 10% H₂SO₄ aqueous solution (40 mL) was cautiously added a solution of NaNO₂ (687 mg, 9.96 mmol) in water (3 mL). The mixture was stirred for 30 min at 0° C., and then sulfamic acid was added to destroy excess nitrous acid. The suspension was filtered, and the filtrate was poured into 10% H₂SO₄ aqueous solution (100 mL) and toluene (50 mL). The mixture was stirred for 3 days at room temperature. The aqueous layer was separated, and extracted with EtoAc (5×30 mL). The combined organic extracts were washed with brine (100 mL), dried over MgSO₄, filtered, and concentrated. The crude product was purified by column chromatography on silica gel (EtOAc/hexane, 1:4) to afford a practically pure phenol product 5 (1.11 g, 76% overall yield). C₁₁H₁₂O₂; yellow solid, mp 98-100° C. (lit.^(S2) mp 96-99° C.) (Smith, P. A. S.; Berry, W. L. J. Org. Chem. 1961, 26, 27.); TLC (EtOAc/hexane, 3:7) R_(f)=0.37; ¹H NMR (600 MHz, CDCl₃) δ 7.33 (1H, d, J=2.8 Hz), 7.07 (1H, d, J=8.2 Hz), 6.94 (1H, dd, J=8.2, 2.8 Hz), 6.27 (1H, s, OH), 2.84 (2H, t, J=5.7 Hz), 2.72 (2H, t, J=6.4 Hz), 1.86-1.76 (4H, m); ¹³C NMR (150 MHz, CDCl₃) δ 206.7, 154.7, 139.2, 133.9, 131.3, 119.8, 114.9, 40.8, 31.6, 25.3, 20.8.

3-Benzyloxy-6,7,8,9-tetrahydrobenzo[7]annulen-5-one (6)

A solution of compound 5 (1.25 g, 7.1 mmol) in anhydrous DMF (10 mL) was treated with potassium carbonate (2.1 g, 15.2 mmol) and benzyl bromide (1 mL, 8.4 mmol). The suspension was vigorously stirred for 24 h at room temperature. The mixture was poured into water (20 mL) and extracted with Et₂O (4×30 mL). The combined organic extracts were washed with water (3×20 mL) and brine (100 mL), dried over MgSO₄, filtered, and concentrated. The crude product was purified by column chromatography on silica gel (EtOAc/hexane, 1:9) to afford a pure benzyloxy product 6 (1.85 g, 98%). C₁₈H₁₈O₂; pale yellow oil; TLC (EtOAc/hexane, 1:9) R_(f)=0.37; ¹H NMR (600 MHz, CDCl₃) δ 7.41 (2H, d, J=7.2 Hz), 7.37-7.35 (3H, m), 7.31 (1H, d, J=7.4 Hz), 7.10 (1H, d, J=8.3 Hz), 7.02 (1H, dd, J=8.3, 2.9 Hz), 5.06 (2H, s), 2.86 (2H, t, J=5.8 Hz), 2.71 (2H, t, J=6.2 Hz), 1.84-1.78 (4H, m); ¹³C NMR (150 MHz, CDCl₃) δ 205.6, 157.4, 139.5, 136.7, 134.2, 131.0, 128.5 (2×), 127.9, 127.5 (2×), 119.7, 113.2, 70.1, 40.7, 31.6, 25.3, 20.8.

3-Benzyloxy-7,8,9,10-tetrahydro-5H-benzo[8]annulen-6-one (7)

A solution of (trimethylsilyl)diazomethane (5 mL, ca. 2 M solution in hexane, 10 mmol) in CH₂Cl₂ (10 mL) was added dropwise over 1 h to a stirred solution of compound 6 (1.6 g, 6 mmol) and BF₃.OEt₂ (820 μL, 10 mmol) in CH₂Cl₂ (20 mL) at 0° C. The mixture was stirred for 12 h at 0° C., and then poured into crushed ice. The aqueous layer was extracted with CH₂Cl₂ (3×20 mL). The combined organic extracts were washed with brine (50 mL), dried over MgSO₄, and concentrated to give an orange oil, which was purified by column chromatography on silica gel (EtOAc/hexane, 1:19) to afford the pure cyclooctanone product 7 (1.23 g, 73%). C₁₉H₂₀O₂; colorless oil; TLC (EtOAc/hexane, 1:9) R_(f)=0.29; ¹H NMR (600 MHz, CDCl₃) δ 7.40 (2H, d, J=7.4 Hz), 7.37-7.34 (2H, m), 7.31-7.29 (1H, m), 7.09 (1H, d, J=8.4 Hz), 6.84 (1H, dd, J=8.4, 2.7 Hz), 6.75 (1H, d, J=2.7 Hz), 5.01 (2H, s), 3.72 (2H, s), 2.74 (2H, t, J=5.8 Hz), 2.31 (2H, t, J=5.3 Hz), 1.81-1.77 (2H, m), 1.72-1.68 (2H, m); ¹³C NMR (150 MHz, CDCl₃) δ 211.8, 157.4, 136.9, 134.7, 133.4, 131.2, 128.5 (2×), 127.9, 127.5 (2×), 116.0, 114.4, 70.0, 48.8, 41.0, 32.3, 31.5, 24.7.

3-Benzyloxy-6-triisopropylsilyloxy-5,6,7,8,9,10-hexahydrobenzo[8]annulene (8)

A solution of compound 7 (4.8 g, 17.1 mmol) in methanol (40 mL) was stirred with NaBH₄ (970 mg, 25.7 mmol) at 0° C. for 1 h, and then concentrated under reduced pressure. The residue was dissolved in CH₂Cl₂ (80 mL), and washed with 1 M HCl aqueous solution (50 mL) and brine (50 mL). The organic layer was dried over MgSO₄, filtered, and concentrated to provide a crude alcohol product as colorless foam (4.8 g).

Triisopropylsilyl trifluoromethanesulfonate (9.2 mL 34.2 mmol) was added dropwise over a period of 3 min to a cold (0° C.) solution of the above-prepared alcohol (4.8 g, 17.0 mmol) and 2,6-lutidine (8 mL, 68.7 mmol) in anhydrous CH₂Cl₂ (50 mL). The mixture was stirred for 1 h at room temperature, and then diluted with CH₂Cl₂ (100 mL). The solution was washed with saturated aqueous NaHCO₃ (50 mL), 1 M HCl aqueous solution (50 mL) and brine (50 mL). The organic layer was dried over MgSO₄, filtered, and concentrated. The residue was purified by column chromatography on silica gel (EtOAc/hexane, 1:9) to afford a pure silyl ether product 8 (7.2 g, 96% overall yield). C₂₈H₄₂O₂Si; colorless syrup; TLC (EtOAc/hexane, 1:9) R_(f)=0.51; ¹H NMR (600 MHz, CDCl₃) δ 7.41 (2H, d, J=7.4 Hz), 7.37-7.34 (2H, m), 7.31-7.28 (1H, m), 6.99 (1H, dd, J=6.6, 2.5 Hz), 6.75-6.74 (2H, m), 5.01 (2H, s), 3.96-3.93 (1H, m), 2.91-2.83 (2H, m), 2.77-2.72 (1H, m), 2.65-2.61 (1H, m), 1.76-1.72 (1H, m), 1.71-1.64 (1H, m), 1.50-1.41 (3H, m), 1.18-1.15 (1H, m), 1.07-1.05 (21H, m); ¹³C NMR (150 MHz, CDCl₃) δ 156.8, 138.5, 137.3, 134.1, 130.1, 128.5 (2×), 127.8, 127.5 (2×), 116.7, 112.5, 73.8, 70.0, 40.9, 34.5, 32.3, 32.0, 20.8, 18.2 (6×), 12.4 (3×).

3-Hydroxy-6-triisopropylsilyloxy-5,6,7,8,9,10-hexahydrobenzo[8]annulene-2-carbaldehyde (9)

A solution of compound 8 (7.1 g, 16.2 mmol) in methanol (50 mL) and EtOAc (20 mL) was treated with Pd/C (100 mg) under an atmosphere of hydrogen. After stirring for 1 h, the mixture was filtered through Celite, and rinsed with EtOAc. The filtrate was concentrated to give a light brown syrup (5.6 g), which was treated with anhydrous MgCl₂ (4.64 g, 48.6 mmol), triethylamine (13.5 mL, 97.2 mmol) and paraformaldehyde (4.86 g, 162 mmol) in anhydrous acetonitrile (150 mL). The suspension was heated at reflux for 12 h. The mixture was cooled to room temperature, and the resulting deep-yellow suspension was acidified with 1 M HCl aqueous solution (200 mL). The solution was extracted with EtOAc (5×150 mL). The combined organic extracts were washed with brine (200 mL), dried over MgSO₄, filtered, and concentrated. The crude product was purified by column chromatography on silica gel (EtOAc/hexane, 1:19) to afford a pure salicylaldehyde product 9 (5.3 g, 87% for two steps). C₂₂H₃₆O₃Si; pale yellow syrup; TLC (EtOAc/hexane, 1:9) R_(f)=0.71; ¹H NMR (600 MHz, CDCl₃) δ 10.77 (1H, s), 9.79 (1H, s), 7.24 (1H, s), 6.76 (1H, s), 4.03-3.99 (1H, m), 2.94-2.88 (2H, m), 2.81-2.76 (1H, m), 2.71-2.67 (1H, m), 1.80-1.75 (1H, m), 1.72-1.66 (1H, m), 1.52-1.46 (2H, m), 1.43-1.38 (1H, m), 1.24-1.16 (1H, m), 1.07-1.05 (21H, m); ¹³C NMR (150 MHz, CDCl₃) δ 195.9, 159.5, 148.2, 133.8, 133.7, 119.5, 118.8, 73.2, 41.0, 34.4, 32.2, 32.1, 20.6, 18.1 (6×), 12.4 (3×).

Ethyl 6,7,8,9,10,11-hexahydro-2-oxo-10-triisopropylsilyloxy-2H-cycloocta[g]chromene-3-carboxylate (10)

A solution of compound 9 (3.6 g, 9.57 mmol) and diethyl malonate (2.88 mL, 19.0 mmol) in ethanol (30 mL) was treated piperidine (0.3 mL, 3.03 mmol) and glacial AcOH (0.1 mL, 1.73 mmol). The mixture was heated at reflux for 4 h, and then cooled to room temperature. The mixture was concentrated, and purified by column chromatography on silica gel (EtOAc/hexane, 1:9) to afford a pure coumarin product 10 (3.75 g, 83%). C₂₇H₄₀O₃Si; white solid, mp 91-93° C.; TLC (EtOAc/hexane, 1:9) R_(f)=0.20; ¹H NMR (600 MHz, CDCl₃) δ 8.45 (1H, s), 7.30 (1H, s), 7.14 (1H, s), 4.38 (2H, q, J=7.1 Hz), 4.05-4.02 (1H, m), 3.03-2.96 (2H, m), 2.87-2.82 (1H, m), 2.78-2.76 (1H, m), 1.76-1.74 (1H, m), 1.69-1.59 (2H, m), 1.48-1.44 (2H, m), 1.38 (3H, t, J=7.1 Hz), 1.19-1.16 (1H, m), 1.11-1.03 (21H, m); ¹³C NMR (150 MHz, CDCl₃) δ 163.4, 157.2, 153.4, 148.6, 145.6, 139.0, 129.2, 118.0, 117.1, 116.4, 73.1, 61.8, 41.0, 34.5, 32.4, 32.0, 20.6, 18.1 (6×), 14.2, 12.4 (3×).

10-Hydroxy-6,7,8,9,10,11-hexahydro-cycloocta[g]chromene-2-one (11)

A solution of compound 10 (473 mg, 1 mmol) in conc. HCl (5 mL) and acetic acid (5 mL) was heated at reflux for 12 h. The mixture was concentrated under reduced pressure. The residue was purified by column chromatography on silica gel (EtOAc/hexane, 1:3) to afford a pure coumarin product 11 (213 mg, 87%) as a colorless solid.

6,7,8,9-Tetrahydro-11H-cycloocta[g]chromene-2,10-dione (12)

A solution of dimethylsulfoxide (0.25 mL, 3.52 mmol) in CH₂Cl₂ (3 mL) was added dropwise to a stirred solution of oxalyl chloride (0.15 mL, 1.77 mmol) in CH₂Cl₂ (3 mL) at −78° C. under nitrogen atmosphere. The solution was stirred for 30 min at −78° C., and then a solution of the alcohol 11 (300 mg, 1.23 mmol) in CH₂Cl₂ (15 mL) was added. The mixture was stirred for additional 30 min at −78° C., and then triethylamine (1.2 mL, 8.6 mmol) was added. The mixture was allowed to warm to room temperature for 30 min, and then poured into water (20 mL). The mixture was extracted with CH₂Cl₂ (3×20 mL). The combined organic extracts were washed with water (30 mL) and brine (30 mL), dried over MgSO₄, filtered, and concentrated. The residue was purified by column chromatography on silica gel (EtOAc/hexane, 1:4) to afford a pure oxo-coumarin product 12 (253 mg, 85%) as a colorless solid.

10,11-Dehydro-6,7,8,9-tetrahydro-cycloocta[g]chromen-2-one (1)

KHMDS (0.5 M solution in toluene, 2.2 mL, 1.1 mmol) was added dropwise to solution of compound 12 (242 mg, 1 mmol) in anhydrous THF (20 mL) at −78° C. After stirring for 30 min at −78° C., a solution of N-phenylbis(trifluoromethanesulfonimide) (Tf₂NPh, 375 mg, 1.05 mmol) in THF (2 mL) was added dropwise. The mixture was allowed to warm to 0° C. and stirred for 30 min. KHMDS (0.5 M solution in toluene, 2.2 mL, 1.1 mmol) was added dropwise to the mixture again. After stirring for 1 h at 0° C., the mixture was diluted with EtOAc (30 mL), and washed with saturated aqueous solution of NaHCO₃ (20 mL) and brine (20 mL). The organic layer was dried over MgSO₄, filtered, and concentrated. The residue was purified by column chromatography on silica gel ((EtOAc/hexane, 1:4) to afford a pure coumarin-fused cyclooctyne 1 (137 mg, 61% overall yield) as a colorless solid.

Ethyl(E)-3-(7-hydroxy-2-oxo-2H-chromen-3-yl)-acrylate (13)

Diethyl glutaconate (4.5 mL, 32 mmol) was added to a solution of 2,4-dihydroxybenzaldehyde (4.14 g, 30 mmol) in methanol (90 mL), followed by addition of 6 drops of piperidine. The mixture was heated at reflux for 24 h, allowed to cool slowly to room temperature, and then chilled to −20° C. The yellow solids were filtered, rinsed with diethyl ether, and dried to yield the desired coumarin compound 13 (7.02 g, 90%). C₁₄H₁₂O₅; pale-yellow solid; TLC (EtOAc/hexane, 3:7) R_(f)=0.25; ¹H NMR (600 MHz, CD₃OD) δ 8.13 (1H, s), 7.55 (1H, dd, J=16.5, 0.6 Hz), 7.51 (1H, d, J=8.6 Hz), 6.91 (1H, d, J=16.5 Hz), 6.79 (1H, dd, J=8.6, 2.4 Hz), 6.70 (1H, d, J=2.4, 0.6 Hz), 4.22 (2H, q, J=6.9 Hz), 1.30 (3H, t, J=6.9 Hz).

Ethyl(E)-3-[7-(trimethylsilyl)ethynyl-2-oxo-2H-chromen-3-yl]-acrylate (15)

To a cold (0° C.) solution of hydroxycoumarin 13 (7.02 g, 27 mmol) and pyridine (11.8 mL, 145.8 mmol) in CH₂Cl₂ (150 mL) was added Tf₂O (11.8 mL, 70.2 mmol). After stirring for 16 h at room temperature, the mixture was diluted with CH₂Cl₂ (150 mL), and washed with 1 M HCl aqueous solution (100 mL) and saturated NaHCO₃ aqueous solution (100 mL). The organic layer was dried over MgSO₄, filtered, and concentrated. The residue was purified by chromatography on a short silica gel column with elution of CH₂Cl₂ to afford a triflate product 14 (9.0 g, 85%).

A mixture of the above-prepared coumarin triflate (9.0 g, 22.9 mmol), PdCl₂(PPh₃)₂ (0.801 g, 1.14 mmol) and CuI (0.432 g, 2.27 mmol) in anhydrous DMF (100 mL) was flushed with nitrogen for about 1 h. Diisopropylethylamine (7.5 mL) was added. The mixture was heated to 90° C., and then trimethylsilylacetylene (4.9 mL, 35 mmol) was added dropwise. After stirring for 2 h at 90° C., the mixture was concentrated under reduced pressure. The crude product was purified by column chromatography on silica gel (CH₂Cl₂/hexane, 1:1) to afford a coupling product 15 (5.53 g, 71%) as a pale-yellow solid.

7-(Trimethylsilyl)ethynyl-2-oxo-2H-chromene-3-carbaldehyde (16)

Ozone was bubbled through a solution of ethyl ester 15 (1.04 g, 3.06 mmol) at −78° C. The yellow color of solution faded in about 5 min. Oxygen was bubbled through the solution for 10 min, followed by addition of dimethylsulfide (0.8 mL, 10.82 mmol) in one portion. The mixture was allowed to warm to room temperature, and stirred for additional 6 h. The mixture was concentrated under reduced pressure. The residue was purified by column chromatography on silica gel (EtOAc/hexane, 1:4) to afford the desired 3-formyl coumarin 16 (720 mg, 87%). C₁₅H₁₄O₃Si; pale-yellow solid; TLC (EtOAc/hexane, 3:7) R_(f)=0.51; ¹H NMR (600 MHz, CDCl₃) δ 10.22 (1H, s), 8.35 (1H, s), 7.58 (1H, d, J=8.0 Hz), 7.42 (1H, s), 7.38 (1H, d, J=8.1 Hz), 0.26 (9H, s).

(E)-7-ethynyl-3-[N-(4-sulfonatobutyl)-3,3-dimethyl-3H-indolium-2-yl]ethenyl-2H-chromen-2-one (C)

Pyrrolidine (83 μL, 1 mmol) was added to a suspension of 3-formyl coumarin 16 (135 mg, 0.5 mmol) and sulfonated indolium salt 17 (147 mg, 0.5 mmol) in ethanol (10 mL). The mixture was stirred for 24 h at room temperature, and then concentrated under reduced pressure to dryness. The residue was purified by column chromatography on silica gel (CH₂Cl₂/MeOH, 1:5 to 1:2) to afford an intermediate product (123 mg, 45%).

Tetrabutylammonium fluoride (1 M solution in THF, 0.46 mL, 0.46 mmol) was added to a solution of the above-prepared intermediate compound (123 mg, 0.23 mmol) in methanol (10 mL) at 0° C. The mixture was stirred for 2 h at 0° C., and then concentrated under reduced pressure. The residue was purified by column chromatography (CH₂Cl₂/MeOH, 1:3) to afford the desired product C (61 mg, 56%) as deep-red solid.

3-Amino-6,7,8,9-tetrahydrobenzocyclohepten-5-one (S1)

A mixture of nitro compound 4 (2.05 g, 10 mmol) and Sn (8.31 g, 70 mmol) in concentrated HCl (45 mL) and ethanol (25 mL) was heated at reflux for 50 min. The mixture was cooled to room temperature, and basified with 30% NaOH aqueous solution. The mixture was filtered through a pad of Celite, and washed with ethanol. The filtrate was extracted with EtOAc (5×50 mL). The combined organic extracts were washed with brine (100 mL), dried over MgSO₄, filtered, and concentrated under reduced pressure to afford the analytically pure amino product S1 (1.44 g, 82%). C₁₁H₁₃NO, yellowish solid, mp 102-104° C. (lit.^([S1]) mp 103-105° C.); TLC (EtOAc/hexane, 3:7) R_(f)=0.29; ¹H NMR (600 MHz, CDCl₃) δ 7.02 (1H, d, J=2.6 Hz), 6.96 (1H, d, J=8.0 Hz), 6.72 (1H, dd, J=8.0, 2.6 Hz), 3.65 (2H, br s, NH), 2.79 (2H, t, J=5.5 Hz), 2.67 (2H, t, J=6.6 Hz), 1.81-1.74 (4H, m); ¹³C NMR (150 MHz, CDCl₃) δ 206.2, 144.9, 139.3, 131.6, 130.7, 118.8, 114.5, 40.8, 31.5, 25.4, 20.9; HRMS calcd for C₁₁H₁₄NO: 176.1070. found: m/z 176.1069 [M+H]⁺.

10-Benzyl-6,7,8,9-tetrahydro-cyclooctatriazolo[5,4-g]chromen-2 (2H)-one (1-A)

A solution of compound 1 (50 mg, 0.22 mmol) in CH₃CN (5 mL) was treated with benzyl azide (44 μL, 0.33 mmol). After stirring for 2 h at room temperature, the mixture was concentrated under reduced pressure. The residue was purified by column chromatography on silica gel (EtOAc/hexane, 3:7) to afford the desired triazole product 1-A (75 mg, 95%). C₂₂H₁₉N₃O₂, colorless solid, mp 60-62° C.; TLC (EtOAc/hexane, 1:1) R_(f)=0.35; ¹H NMR (600 MHz, CDCl₃) δ 7.75 (1H, s), 7.65 (1H, d, J=9.4 Hz), 7.37-7.32 (3H, m), 7.24 (1H, s), 7.20-7.19 (2H, m), 6.39 (1H, d, J=9.4 Hz), 5.50 (2H, s), 2.69-2.67 (2H, m), 2.65-2.63 (2H, m), 1.79-1.75 (2H, m), 1.67-1.64 (2H, m); ¹³C NMR (150 MHz, CDCl₃) δ 161.0, 152.4, 143.1, 136.1, 135.3, 135.0, 134.4, 129.0 (2×), 128.7, 128.4, 128.1, 127.1 (2×), 126.9, 116.7, 116.4, 51.9, 30.8, 30.6, 23.9, 20.0; HRMS calcd for C₂₂H₂₀N₃O₂: 358.1550. found: m/z 358.1548 [M+H]⁺.

N-[2-(11-Oxo-4,6,7,11-tetrahydrochromeno[7′,6′:3,4]cycloocta[1,2-d][1,2,3]triazol-3 (5H)-yl)]acetamido-2-deoxy-α,β-D-mannopyranose (1-B)

A solution of compound 1 (50 mg, 0.22 mmol) in MeOH (5 mL) and water (1 mL) was treated with N-azidoacetylmannosamine (142 mg, 0.33 mmol). After stirring for 2 h at room temperature, the mixture was concentrated under reduced pressure. The residue was purified by column chromatography on silica gel (MeOH/CH₂Cl₂, 1:9) to afford the desired triazole product 1-B (98 mg, 92%). C₂₃H₂₆N₄O₈, colorless solid, mp 170-172° C. (dec.); TLC (MeOH/CH₂Cl₂, 1:8) R_(f)=0.25; ¹H NMR (600 MHz, DMSO-d₆) δ 8.04 (1H, d, J=9.5 Hz), 7.59 (1H, s), 7.52 (1H, s), 6.48 (1H, d, J=9.5 Hz), 5.15 (1H, d, J=2.9 Hz), 5.11 (1H, d, J=6.9 Hz), 4.98-4.85 (1H, m), 4.89-4.81 (2H, m), 4.44-4.38 (1H, m), 3.61-3.59 (3H, m), 3.53-3.45 (2H, m), 3.42-3.37 (1H, m), 3.16-3.14 (2H, m), 2.86-2.82 (2H, m), 2.72-2.70 (2H, m), 1.78 (2H, br s), 1.61 (2H, br t, J=5.5 Hz); ¹³C NMR (150 MHz, DMSO-d₆) δ 165.2, 160.1, 151.9, 143.8, 140.6, 137.0, 135.9, 134.7, 128.8, 118.6, 116.1, 115.2, 92.5, 90.4, 72.9, 72.1, 71.0, 70.5, 68.2, 67.5, 61.5, 61.0, 54.7, 54.2, 50.0, 49.9, 30.6, 29.9, 22.8, 19.6; HRMS calcd for C₂₃H₂₇N₄O₈: 487.1829. found: m/z 487.1827 [M+H]+.

Example 2 Detecting and Imaging Biomolecules Spectroscopic Materials and Methods

All spectroscopic measurements of Compound 1 and the triazole products 1-A and 1-B were performed in a mixture of 10% DMSO in PBS buffer (FIG. 11). UV-vis spectra and fluorescence spectra were recorded on a Molecular Devices Spectramax M5 spectrometer. For each experiment, the absorbance spectra were measured within an absorbance range of 0.07 to 0.7 (l=10 cm). Quantum yields were determined from the slope of the integrated fluorescence emission between 360 and 550 nm (excitation at 330 nm) versus absorbance using quinine sulfate (Φ_(f)=0.54±0.0 3)[^(S3)] as fluorescence standard. The quantum yield was calculated as an average of 4 points according to the following equation:

Φ_(sample)=Φ_(standard)(A _(standard) /A _(sample))(F _(sample) /F _(standard))(n _(sample) /n _(standard))²

where “Φ” is the quantum yield, “A” is the absorbance at the excitation frequency, “F” is the area under the emission curve, and “n” is the refractive index of the solvent.

Table 1 in FIG. 6 shows the absorption and fluorescence data of Compounds 1 and triazole products 1-A and 1-B recorded under simulated physiological conditions (PBS buffer containing 10% DMSO, pH 7.4, 37° C.). Formation of triazoles 1-A and 1-B were accompanied by a significant increase in fluorescence intensity with a large Stokes shift into a standard range for coumarin emission (FIG. 8 a). Upon excitation at 330 nm, Compound 1 produced a weak emission band centered at 405 nm with a low quantum yield (Φ_(f)=0.011), whereas both triazoles 1-A and 1-B exhibited a strong fluorescence at 435 nm with a quantum yield of 0.23 and 0.21, respectively.

Time Course Measurements by Fluorescence Spectroscopy

To probe the SPAAC reaction under the conditions that would be more typical for biomolecule labeling, the fluorescence response and time course for the reaction of Compound 1 with N-azidoacetylmannosamine (ManNAz) were investigated. The experiments indicated that more than 90% of ManNAz was consumed in 40 min, and the fluorescence intensity reached a plateau in less than 1 h (FIG. 8 b).

A solution of Compound 1 (30 mol) and N-azidoacetylmannosamine (15 μmol) in a mixture of 10% DMSO in PBS buffer (2.5 mL) was incubated at 37° C. The fluorescence emission intensity at 435 nm upon excitation at 330 nm was monitored in 5 min intervals. For each point the fluorescence intensity was measured over a period of 5 sec and averaged over a total of 3 points. In a control experiment the same conditions were used except that N-acetylmannosamine (15 μmol) was added to the solution.

Kinetics Measurements of Compound (1) by ¹H NMR Experiment I

Compound 1 and benzyl azide were predissolved in CD₃CN, and then mixed at equimolar concentration of 20 mM. The reaction was monitored by ¹H-NMR analysis over a period of 1 h. The concentration of each component was determined, based on the concentration of initial compound 1, by integration at multiple chemical shifts in the ¹H-NMR spectrum. By plotting 1/[1](M⁻¹) vs. time (sec), a second order rate constant in unit of M⁻¹s⁻¹ was determined using linear regression analysis. This procedure was repeated 3 times with a concentrated of 20 mM to afford a rate constant of 0.012 M⁻¹s⁻¹ at 25° C. (FIG. 4B).

Experiment II

Compound 1 and N-azidoacetylmannosamine were predissolved in CD₃OD/D₂O (5:1, v/v), and then mixed at equimolar concentration of 20 mM. The reaction was monitored by ¹H-NMR analysis over a period of 1 h. The concentration of each component was determined, based on the concentration of initial compound 1, by integration at multiple chemical shifts in the ¹H-NMR spectrum. By plotting 1/[1](M⁻¹) vs. time (sec), a second order rate constant in unit of M⁻¹s⁻¹ was determined using linear regression analysis. This procedure was repeated 3 times with a concentrated of 20 mM to afford a rate constant of 0.010 M⁻¹s⁻¹ at 25° C. (FIG. 11).

Example 3 Microscopic Analysis of Fluorescence Labeling in Live Cells

To observe the fluorescence labeled azido-glycoconjugates in cells, CL1-5 cells (a lung cancer cell line) were seeded on chamber slide (2.5×10⁴ cells/0.5 mL per wells) and incubated in culture medium (RPMI-1640 supplemented with 10% FBS, 100 U/mL penicillin, 100 μg/mL streptomycin, 1 mM L-glutamine and 1 mM sodium pyruvate) with either 200 μM control sugar (peracetylated N-acetylmannosamine, Ac₄ManNAc) or azido-sugar (peracetylated azido-N-acetylmannosamine, Ac₄ManNAz) for 3 days.

For Time-lapse imaging of live cells, experiments were carried out using a confocal microscope (TCS-SP5-MP-SMD, Leica) equipped with an incubator to keep the cells in culture conditions. Prewashed cells were incubated with 100 μM compound 1 in PBS buffer with 10% DMSO and images of cell were acquired at 450 nm emission and in 5-min intervals.

For comparing the localization of azido-glycans, probe-labeled cells were washed with PBS, fixed with 3% paraformaldehyde in PBS at room temperature for 20 min, permeablized with 0.2% Triton X-100 in PBS at room temperature for 20 min, and blocked with 3% bovine serum albumin in PBS at room temperature for 30 min. Cells were stained with fluorescein conjugated WGA lectin for Golgi, and propidium iodide (PI) for nucleus (FIG. 12).

Performance of Compound 1 in live cell imaging was investigated. Highly invasive lung cancer cells, CL1-5, were cultured in the presence of peracetylated azido-N-acetylmannosamine (Ac₄ManNAz, 200 μM) for 3 days to metabolically produce the azido-sialic acid expressed cells. As a negative control, CL1-5 cells were grown in the presence of peracetylated N-acetylmannosamine (Ac₄ManNAc, 200 μM). A time course experiment was conducted by treating 100 μM of Compound 1 (once) and conducted by exposing the cells at 5-min intervals under no-wash and no-fixation conditions (FIG. 8 and FIG. 12). The Ac₄ManNAz treated cells showed a time-dependent increase of fluorescence intensity, and the cell labeling was complete after 1.5 h. In contrast, the control cells exhibited almost no fluorescence staining, indicating that background labeling is negligible. Furthermore, the localization of azido-containing glycoconjugates in living cells was visualized by confocal microscopy. The cells labeled by Compound 1 were subsequently stained with fluorescein-conjugated WGA lectin (a Golgi marker) and propidium iodide (PI, a nucleus marker). The blue fluorescent signals derived from the coumarin probe are from labeled sialylated glycans apparently showed in cytosol (FIG. 4), which were partially co-localized with Golgi apparatus staining, but not with nucleus staining.

EQUIVALENTS AND SCOPE

In the claims articles such as “a,” “an,” and “the” may mean one or more than one unless indicated to the contrary or otherwise evident from the context. Claims or descriptions that include “or” between one or more members of a group are considered satisfied if one, more than one, or all of the group members are present in, employed in, or otherwise relevant to a given product or process unless indicated to the contrary or otherwise evident from the context. The present disclosure includes embodiments in which exactly one member of the group is present in, employed in, or otherwise relevant to a given product or process. The present disclosure includes embodiments in which more than one, or all of the group members are present in, employed in, or otherwise relevant to a given product or process.

Furthermore, the present disclosure encompasses all variations, combinations, and permutations in which one or more limitations, elements, clauses, and descriptive terms from one or more of the listed claims is introduced into another claim. For example, any claim that is dependent on another claim can be modified to include one or more limitations found in any other claim that is dependent on the same base claim. Where elements are presented as lists, e.g., in Markush group format, each subgroup of the elements is also disclosed, and any element(s) can be removed from the group. It should it be understood that, in general, where the present disclosure, or aspects of the present disclosure, is/are referred to as comprising particular elements and/or features, certain embodiments of the present disclosure or aspects of the present disclosure consist, or consist essentially of, such elements and/or features. For purposes of simplicity, those embodiments have not been specifically set forth in haec verba herein. It is also noted that the terms “comprising” and “containing” are intended to be open and permits the inclusion of additional elements or steps. Where ranges are given, endpoints are included. Furthermore, unless otherwise indicated or otherwise evident from the context and understanding of one of ordinary skill in the art, values that are expressed as ranges can assume any specific value or sub-range within the stated ranges in different embodiments of the present disclosure, to the tenth of the unit of the lower limit of the range, unless the context clearly dictates otherwise.

This application refers to various issued patents, published patent applications, journal articles, and other publications, all of which are incorporated herein by reference. If there is a conflict between any of the incorporated references and the instant specification, the specification shall control. In addition, any particular embodiment of the present present disclosure that falls within the prior art may be explicitly excluded from any one or more of the claims. Because such embodiments are deemed to be known to one of ordinary skill in the art, they may be excluded even if the exclusion is not set forth explicitly herein. Any particular embodiment of the present disclosure can be excluded from any claim, for any reason, whether or not related to the existence of prior art.

Those skilled in the art will recognize or be able to ascertain using no more than routine experimentation many equivalents to the specific embodiments described herein. The scope of the present embodiments described herein is not intended to be limited to the above Description, but rather is as set forth in the appended claims. Those of ordinary skill in the art will appreciate that various changes and modifications to this description may be made without departing from the spirit or scope of the present present disclosure, as defined in the following claims.

REFERENCES

-   Bach, R. D. J. Am. Chem. Soc. 2009, 131, 5233-5243. -   Best, M. D. Biochemistry 2009, 48, 6571-6584. -   Jewett et al. Chem. Soc. Rev. 2010, 39, 1272-1279. -   Kolb et al. Angew. Chem., Int. Ed. 2001, 40, 2004-2021. -   Ning et al. Angew. Chem. Int. Ed. 2008, 47, 2253-2255. -   Prescher et al. Nat. Chem. Bio. 2005, 1, 13-21. -   Qi et al. Bioconjugate Chem. 2011, 22, 1758-1762. -   Sletten, E. M. et al. Angew. Chem. Int. Ed. 2009, 48, 2-27. -   Zhou, Z.; et al. J. Am. Chem. Soc. 2004, 126, 8862-8863. -   J. N. Demas et al., J. Phys. Chem. 1971, 75, 991-1024. -   J. A. Prescher, C. R. Bertozzi, Nat. Chem. Biol. 2005, 1, 13-21. -   K. T. Barglow et al., Nat. Methods 2007, 4, 822-827. -   R. K. V. Lim et al., Chem. Commun. 2010, 46, 1589-1600. -   A. Niederwieser et al., Angew. Chem. 2013, 125, 4359-4363; Angew.     Chem. Int. Ed. 2013, 52, 4265-4268. -   C. W. Tomoe et al., J. Org. Chem., 2002, 67, 3057-3064. -   P. Wu et al., Aldrichim. Acta 2007, 40, 7-17. -   J. M. Baskin, C. R. Bertozzi, QSAR Comb. Sci. 2007, 26, 1211-1219. -   C.-S. Tsai et al., Proc. Natl. Acad. Sci. U.S.A. 2013, 110,     2466-2471. -   C. Le Droumaguet et al., Chem. Soc. Rev. 2010, 39, 1233-1239. -   C. Wang et al., Sci. China Chem. 2012, 55, 125-130. -   P. Shieh et al., Am. Chem. Soc. 2012, 134, 17428-17431. -   X. Ning et al., Angew. Chem. 2008, 120, 2285-2287. -   H. Stöckmann et al., Chem. Sci. 2011, 2, 932-936. -   J. Dommerholt et al., Angew. Chem. 2010, 122, 9612-9615. -   G. de Almeida et al., Angew. Chem. 2012, 124, 2493-2497. -   G. de Almeida et al., Angew. Chem. Int. Ed. 2012, 51, 2443-2447. -   M. King et al., Chem. Commun. 2012, 48, 9308-9309. -   J. C. Jewett et al., Org. Lett. 2011, 13, 5937-5939. -   F. Friscourt et al., J. Am. Chem. Soc. 2012, 134, 18809-18815. -   A. P. de Silva et al., Chem. Rev. 1997, 97, 1515-1566.

All publications and patent applications cited in this specification are herein incorporated by reference as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.

Although the foregoing present disclosure has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be readily apparent to those of ordinary skill in the art in light of the teachings of this present disclosure that certain changes and modifications may be made thereto without departing from the spirit or scope of the appended claims. 

1-43. (canceled)
 44. A compound of Formula (I):

or a salt thereof, wherein X₁, X₂, X₃, and X₄ are in a 8-membered carbocycle or heterocycle; provided that when the 8-membered ring is a heterocycle, three of X₁, X₂, X₃, and X₄ are carbon atoms, and one of X₁, X₂, X₃, and X₄ is N, O, P, or S; each of G¹, G², G³ and G⁴ is independently selected from hydrogen, halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, ═O, ═NOH, ═N—OR^(A), ═N—NH₂, ═N—NHR^(B), ═N—N(R^(B))₂, and —NHSO₂R^(A); or G¹ and G² are taken together with their intervening atoms to form an optionally substituted carbocycle or heterocycle; or G³ and G⁴ are taken together with their intervening atoms to form an optionally substituted carbocycle or heterocycle; each of G⁵ and G⁸ is independently selected from hydrogen, halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteoaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A); each of G⁶ and G⁷ is independently selected from hydrogen, halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteoaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A), or G⁶ and G⁷ are taken together with their intervening atoms to form an optionally substituted carbocycle or heterocycle; each instance of R^(A) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, or optionally substituted heteroaryl, or an oxygen protecting group when attached to an oxygen, or a sulfur protecting group when attaching to sulfur; each instance of R^(B) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, or optionally substituted heteroaryl, k or a nitrogen protecting group, or two R^(B) taken together with the intervening nitrogen form a heterocycle; each instance of R^(C) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, or optionally substituted heteroaryl; and provided that when G¹ and G² are taken together with their intervening atoms to form an optionally substituted phenyl, G⁶ and G⁷ are taken together with their intervening atoms to form an optionally substituted heterocycle and X⁴ is not N.
 45. The compound of claim 44, wherein X¹—X² is —CH═CH—.
 46. The compound of claim 44, wherein X³—X⁴ is —CH═CH—.
 47. The compound of any one of claims 44-46, wherein G⁶ and G⁷ are taken together with their intervening atoms to form an optionally substituted heterocycle.
 48. The compound of claim 44, wherein the compound is of Formula (II)

or a salt thereof, wherein each of G⁹ and G¹⁰ is independently selected from hydrogen, halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted heteoaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A).
 49. The compound of claim 48, wherein X¹—X² is —CH═CH—.
 50. The compound of claim 48, wherein X³—X⁴ is —CH═CH—.
 51. The compound of any one of claims 48-50, wherein G⁹ is hydrogen and G¹⁰ is optionally substituted alkenyl.
 52. The compound of claim 51, wherein G¹⁰ is of Formula (G-i).


53. The compound of claim 48, wherein the compound is one of the compounds listed in Table
 1. 54. The compound of claim 48, wherein the compound is one of the formulae:


55. The compound of claim 54, wherein the compound is of the formula


56. A compound of one of the following formulae:

or a salt thereof, wherein X₁, X₂, X₃, and X₄ are in a 8-membered carbocycle or heterocycle; provided that when the 8-membered ring is a heterocycle, three of X, X₂, X₃, and X₄ are carbon atoms, and one of X₁, X₂, X₃, and X₄ is N, O, P, or S; each of G¹, G², G³ and G⁴ is independently selected from hydrogen, halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(A), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, ═O, ═NOH, ═N—OR^(A), ═N—NH₂, ═N—NHR^(B), ═N—N(R^(B))₂, and —NHSO₂R^(A); or G¹ and G² are taken together with their intervening atoms to form an optionally substituted carbocycle or heterocycle; or G³ and G⁴ are taken together with their intervening atoms to form an optionally substituted carbocycle or heterocycle; each of G⁵ and G⁸ is independently selected from hydrogen, halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteoaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A); each of G⁶ and G⁷ is independently selected from hydrogen, halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteoaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A), or G⁶ and G⁷ are taken together with their intervening atoms to form an optionally substituted carbocycle or heterocycle; each of G⁹ and G¹⁰ is independently selected from hydrogen, halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted heteoaryl, —OR^(A), —CH₂OR^(A), —OC(O)R^(C), —SR^(A), —N(R^(B))₂, —N(R^(B))C(O)R^(C), —C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A). each of R¹¹ and R¹² is independently selected from the group consisting of hydrogen, halogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteoaryl, optionally substituted heterocyclylalkyl, optionally substituted arylalkyl, optionally substituted heteoarylalkyl, —OR^(A), —CH₂OR^(A), —(CH₂)_(t)OC(O)R^(C), —SR^(A), —N(R^(B))₂, —(CH₂)_(t)—N(R^(B))C(O)R^(C), —(CH₂)_(t)—C(O)N(R^(B))₂, —CN, —NO₂, —C(O)R^(C), —(CH₂)_(t)C(O)OR^(A), —S(O)R^(C), —SO₂R^(A), —SO₂N(R^(B))₂, and —NHSO₂R^(A); t is an integer of 1 to 5, inclusive; each instance of R^(A) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, or an oxygen protecting group when attached to an oxygen, or a sulfur protecting group when attaching to sulfur; each instance of R^(B) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, or a nitrogen protecting group, or two R^(B) taken together with the intervening nitrogen form a heterocycle; each instance of R^(C) is independently hydrogen, optionally substituted C₁-C₆ alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted heterocyclyl, optionally substituted aryl, or optionally substituted heteroaryl; and provided that when G¹ and G² are taken together with their intervening atoms to form an optionally substituted phenyl, G⁶ and G⁷ are taken together with their intervening atoms to form an optionally substituted heterocycle and X⁴ is not N.
 57. A compound of claim 44 or claim 56, wherein

is —CH₂—CH₂—CH₂—CH₂—.
 58. A method for detecting an azide-containing molecule comprising (a) incubating a compound of claim 44 with a sample containing the azide-containing molecule under conditions allowing for ligation of the compound to an azido group of the molecule to form a triazole product; and (b) detecting a fluorescent signal released from the triazole product.
 59. The method of claim 58, wherein the incubating step is carried out in the absence of a metal catalyst.
 60. The method of claim 58, wherein the compound is covalently linked to the azido group.
 61. The method of claim 58, wherein the sample contains cells and the azide-containing molecule is located on or inside the cells.
 62. The method of claim 58, wherein the compound is of Formula (I) or Formula (II).
 63. The method of any one of claims 58-62, wherein the azide-containing molecule is a biomolecule.
 64. The method of claim 63, wherein the biomolecule is a DNA, RNA, protein or glycan.
 65. The method of claim 63, wherein the biomolecule is on a cell surface.
 66. The method of claim 63, wherein the biomolecule is intracellular.
 67. The method of claim 63, wherein the biomolecule is of avian, mammalian, viral, parasitical, fungal, or bacterial origin.
 68. The method of claim 67, wherein the biomolecule is of human origin.
 69. The method of claim 63, wherein the presence or absence of the biomolecule as measured by the imaging of the fluorescence signal is indicative of a disease state or physical condition.
 70. The method of claim 68, wherein the disease is cancer or inflammation.
 71. The method of claim 70, wherein the disease is rheumatoid arthritis.
 72. The method of claim 58, wherein the molecule is an organic molecule.
 73. A method for detecting an azide-containing molecule in a sample, comprising: (a) contacting a compound of claim 44 to a sample suspected of having an azide-containing molecule; (b) detecting a level of a fluorescent signal released from the sample by fluorescence imaging, and (c) determining presence of the azide-containing molecule in the sample, wherein an enhanced fluorescent signal as compared to a level of the fluorescent signal in the absence of the compound indicates presence of the azide-containing molecule. 